dmc

dynamic mail client
git clone git://git.suckless.org/dmc
Log | Files | Refs | README | LICENSE

commit e4be3727d9a3ba27dc2d67b7dcfdc07ae372e00d
Author: pancake@localhost.localdomain <unknown>
Date:   Sat, 10 Oct 2009 14:47:14 +0200

* Initial import of 'dmc' into mercurial
Diffstat:
README | 61+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
doc/imap-rfc3501.txt | 4830+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
doc/pop3-rfc1939.txt | 1291+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
doc/smtp-rfc821.txt | 2707+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/Makefile | 10++++++++++
src/dmc | 10++++++++++
src/imap4.c | 107+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/pop3.c | 93+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 9109 insertions(+), 0 deletions(-)

diff --git a/README b/README @@ -0,0 +1,61 @@ + +-----+---------------------+ + | DMC | Dynamic Mail Client | + +-----+---------------------+ + +Sending mails: +-------------- + dmc-smtp ~/mail/outbox/001.eml + [ $? = 0 ] && mv ~/mail/outbox/001.* ~/mail/sent/ + + +IMAP handling: +-------------- + Usage: dmc-imap [options] [host] [port] < commands > output + dmc-imap -a plain -d ~/mail [host] [port] + + options: + -a : auth method + -d : base user mail directory + + commands: + cd [folder] + # SELECT "folder" + 1003 [20:47:15] IMAP4> 51 SELECT "Sent Messages" + 1004 [20:47:15] IMAP4< * FLAGS (\Answered \Flagged \Deleted \Seen \Draft $Forwarded) + 1005 [20:47:15] IMAP4< * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft $Forwarded \*)] Flags permitted. + 1006 [20:47:15] IMAP4< * 340 EXISTS + 1007 [20:47:15] IMAP4< * 2 RECENT + 1008 [20:47:15] IMAP4< * OK [UIDVALIDITY 1230118148] UIDs valid + 1009 [20:47:15] IMAP4< * OK [UIDNEXT 341] Predicted next UID + 1010 [20:47:15] IMAP4< 51 OK [READ-WRITE] Select completed. + + st : show status + 2508 [20:48:11] IMAP4> 60 STATUS "Spam.learn-ham" (MESSAGES UIDNEXT UIDVALIDITY UNSEEN) + 2509 [20:48:12] IMAP4< * STATUS "Spam.learn-ham" (MESSAGES 0 UIDNEXT 1 UIDVALIDITY 1211795420 UNSEEN 0) + 2510 [20:48:12] IMAP4< 60 OK Status completed. + + ls [num] : list num mails (can be used to check for new mail) + cp = copy a mail from one folder to other + mv = copy+remove + rm = remove mail + lt = list folder tree + +LOGIN + Example: C: a001 LOGIN SMITH SESAME + S: a001 OK LOGIN completed +SELECT + Example: C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: A142 OK [READ-WRITE] SELECT completed +CREATE + Example: C: A003 CREATE owatagusiam/ + S: A003 OK CREATE completed + C: A004 CREATE owatagusiam/blurdybloop + S: A004 OK CREATE completed + diff --git a/doc/imap-rfc3501.txt b/doc/imap-rfc3501.txt @@ -0,0 +1,4830 @@ + + [ _R_F_C_ _I_n_d_e_x | _R_F_C_ _S_e_a_r_c_h | _U_s_e_n_e_t_ _F_A_Q_s | _W_e_b_ _F_A_Q_s | _D_o_c_u_m_e_n_t_s | _C_i_t_i_e_s ] + AAlltteerrnnaattee FFoorrmmaattss:: _r_f_c_3_5_0_1_._t_x_t | _r_f_c_3_5_0_1_._t_x_t_._p_d_f + ******** RRFFCC 33550011 -- IINNTTEERRNNEETT MMEESSSSAAGGEE AACCCCEESSSS PPRROOTTOOCCOOLL -- VVEERRSSIIOONN 44rreevv11 ******** +=============================================================================== + * SSeeaarrcchh tthhee AArrcchhiivveess DDiissppllaayy RRFFCC bbyy nnuummbbeerr + * [q [display ] [Display RFC By Number] + ] [Search RFCs] +=============================================================================== + + ************ RRFFCC33550011 -- IINNTTEERRNNEETT MMEESSSSAAGGEE AACCCCEESSSS PPRROOTTOOCCOOLL -- VVEERRSSIIOONN 44rreevv11 ************ + +Network Working Group M. Crispin +Request for Comments: 3501 University of Washington +Obsoletes: 2060 March 2003 +Category: Standards Track + + INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1 + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2003). All Rights Reserved. + +Abstract + + The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1) + allows a client to access and manipulate electronic mail messages on + a server. IMAP4rev1 permits manipulation of mailboxes (remote + message folders) in a way that is functionally equivalent to local + folders. IMAP4rev1 also provides the capability for an offline + client to resynchronize with the server. + + IMAP4rev1 includes operations for creating, deleting, and renaming + mailboxes, checking for new messages, permanently removing messages, + setting and clearing flags, _R_F_C_ _2_8_2_2 and _R_F_C_ _2_0_4_5 parsing, searching, + and selective fetching of message attributes, texts, and portions + thereof. Messages in IMAP4rev1 are accessed by the use of numbers. + These numbers are either message sequence numbers or unique + identifiers. + + IMAP4rev1 supports a single server. A mechanism for accessing + configuration information to support multiple IMAP4rev1 servers is + discussed in _R_F_C_ _2_2_4_4. + + IMAP4rev1 does not specify a means of posting mail; this function is + handled by a mail transfer protocol such as _R_F_C_ _2_8_2_1. + +Table of Contents + + IMAP4rev1 Protocol Specification ................................ 4 + 1. How to Read This Document ............................... 4 + 1.1. Organization of This Document ........................... 4 + 1.2. Conventions Used in This Document ....................... 4 + 1.3. Special Notes to Implementors ........................... 5 + 2. Protocol Overview ....................................... 6 + 2.1. Link Level .............................................. 6 + 2.2. Commands and Responses .................................. 6 + 2.2.1. Client Protocol Sender and Server Protocol Receiver ..... 6 + 2.2.2. Server Protocol Sender and Client Protocol Receiver ..... 7 + 2.3. Message Attributes ...................................... 8 + 2.3.1. Message Numbers ......................................... 8 + 2.3.1.1. Unique Identifier (UID) Message Attribute ....... 8 + 2.3.1.2. Message Sequence Number Message Attribute ....... 10 + 2.3.2. Flags Message Attribute ................................. 11 + 2.3.3. Internal Date Message Attribute ......................... 12 + 2.3.4. [_R_F_C_-_2_8_2_2] Size Message Attribute ....................... 12 + 2.3.5. Envelope Structure Message Attribute .................... 12 + 2.3.6. Body Structure Message Attribute ........................ 12 + 2.4. Message Texts ........................................... 13 + 3. State and Flow Diagram .................................. 13 + 3.1. Not Authenticated State ................................. 13 + 3.2. Authenticated State ..................................... 13 + 3.3. Selected State .......................................... 13 + 3.4. Logout State ............................................ 14 + 4. Data Formats ............................................ 16 + 4.1. Atom .................................................... 16 + 4.2. Number .................................................. 16 + 4.3. String .................................................. 16 + 4.3.1. 8-bit and Binary Strings ................................ 17 + 4.4. Parenthesized List ...................................... 17 + 4.5. NIL ..................................................... 17 + 5. Operational Considerations .............................. 18 + 5.1. Mailbox Naming .......................................... 18 + 5.1.1. Mailbox Hierarchy Naming ................................ 19 + 5.1.2. Mailbox Namespace Naming Convention ..................... 19 + 5.1.3. Mailbox International Naming Convention ................. 19 + 5.2. Mailbox Size and Message Status Updates ................. 21 + 5.3. Response when no Command in Progress .................... 21 + 5.4. Autologout Timer ........................................ 22 + 5.5. Multiple Commands in Progress ........................... 22 + 6. Client Commands ........................................ 23 + 6.1. Client Commands - Any State ............................ 24 + 6.1.1. CAPABILITY Command ..................................... 24 + 6.1.2. NOOP Command ........................................... 25 + 6.1.3. LOGOUT Command ......................................... 26 + + 6.2. Client Commands - Not Authenticated State .............. 26 + 6.2.1. STARTTLS Command ....................................... 27 + 6.2.2. AUTHENTICATE Command ................................... 28 + 6.2.3. LOGIN Command .......................................... 30 + 6.3. Client Commands - Authenticated State .................. 31 + 6.3.1. SELECT Command ......................................... 32 + 6.3.2. EXAMINE Command ........................................ 34 + 6.3.3. CREATE Command ......................................... 34 + 6.3.4. DELETE Command ......................................... 35 + 6.3.5. RENAME Command ......................................... 37 + 6.3.6. SUBSCRIBE Command ...................................... 39 + 6.3.7. UNSUBSCRIBE Command .................................... 39 + 6.3.8. LIST Command ........................................... 40 + 6.3.9. LSUB Command ........................................... 43 + 6.3.10. STATUS Command ......................................... 44 + 6.3.11. APPEND Command ......................................... 46 + 6.4. Client Commands - Selected State ....................... 47 + 6.4.1. CHECK Command .......................................... 47 + 6.4.2. CLOSE Command .......................................... 48 + 6.4.3. EXPUNGE Command ........................................ 49 + 6.4.4. SEARCH Command ......................................... 49 + 6.4.5. FETCH Command .......................................... 54 + 6.4.6. STORE Command .......................................... 58 + 6.4.7. COPY Command ........................................... 59 + 6.4.8. UID Command ............................................ 60 + 6.5. Client Commands - Experimental/Expansion ............... 62 + 6.5.1. X<atom> Command ........................................ 62 + 7. Server Responses ....................................... 62 + 7.1. Server Responses - Status Responses .................... 63 + 7.1.1. OK Response ............................................ 65 + 7.1.2. NO Response ............................................ 66 + 7.1.3. BAD Response ........................................... 66 + 7.1.4. PREAUTH Response ....................................... 67 + 7.1.5. BYE Response ........................................... 67 + 7.2. Server Responses - Server and Mailbox Status ........... 68 + 7.2.1. CAPABILITY Response .................................... 68 + 7.2.2. LIST Response .......................................... 69 + 7.2.3. LSUB Response .......................................... 70 + 7.2.4 STATUS Response ........................................ 70 + 7.2.5. SEARCH Response ........................................ 71 + 7.2.6. FLAGS Response ......................................... 71 + 7.3. Server Responses - Mailbox Size ........................ 71 + 7.3.1. EXISTS Response ........................................ 71 + 7.3.2. RECENT Response ........................................ 72 + 7.4. Server Responses - Message Status ...................... 72 + 7.4.1. EXPUNGE Response ....................................... 72 + 7.4.2. FETCH Response ......................................... 73 + 7.5. Server Responses - Command Continuation Request ........ 79 + + 8. Sample IMAP4rev1 connection ............................ 80 + 9. Formal Syntax .......................................... 81 + 10. Author's Note .......................................... 92 + 11. Security Considerations ................................ 92 + 11.1. STARTTLS Security Considerations ....................... 92 + 11.2. Other Security Considerations .......................... 93 + 12. IANA Considerations .................................... 94 + Appendices ..................................................... 95 + A. References ............................................. 95 + B. Changes from _R_F_C_ _2_0_6_0 .................................. 97 + C. Key Word Index ......................................... 103 + Author's Address ............................................... 107 + Full Copyright Statement ....................................... 108 + +IMAP4rev1 Protocol Specification + +1. How to Read This Document + +1.1. Organization of This Document + + This document is written from the point of view of the implementor of + an IMAP4rev1 client or server. Beyond the protocol overview in + section 2, it is not optimized for someone trying to understand the + operation of the protocol. The material in sections 3 through 5 + provides the general context and definitions with which IMAP4rev1 + operates. + + Sections 6, 7, and 9 describe the IMAP commands, responses, and + syntax, respectively. The relationships among these are such that it + is almost impossible to understand any of them separately. In + particular, do not attempt to deduce command syntax from the command + section alone; instead refer to the Formal Syntax section. + +1.2. Conventions Used in This Document + + "Conventions" are basic principles or procedures. Document + conventions are noted in this section. + + In examples, "C:" and "S:" indicate lines sent by the client and + server respectively. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to + be interpreted as described in [KEYWORDS]. + + The word "can" (not "may") is used to refer to a possible + circumstance or situation, as opposed to an optional facility of the + protocol. + + "User" is used to refer to a human user, whereas "client" refers to + the software being run by the user. + + "Connection" refers to the entire sequence of client/server + interaction from the initial establishment of the network connection + until its termination. + + "Session" refers to the sequence of client/server interaction from + the time that a mailbox is selected (SELECT or EXAMINE command) until + the time that selection ends (SELECT or EXAMINE of another mailbox, + CLOSE command, or connection termination). + + Characters are 7-bit US-ASCII unless otherwise specified. Other + character sets are indicated using a "CHARSET", as described in + [MIME-IMT] and defined in [CHARSET]. CHARSETs have important + additional semantics in addition to defining character set; refer to + these documents for more detail. + + There are several protocol conventions in IMAP. These refer to + aspects of the specification which are not strictly part of the IMAP + protocol, but reflect generally-accepted practice. Implementations + need to be aware of these conventions, and avoid conflicts whether or + not they implement the convention. For example, "&" may not be used + as a hierarchy delimiter since it conflicts with the Mailbox + International Naming Convention, and other uses of "&" in mailbox + names are impacted as well. + +1.3. Special Notes to Implementors + + Implementors of the IMAP protocol are strongly encouraged to read the + IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in + conjunction with this document, to help understand the intricacies of + this protocol and how best to build an interoperable product. + + IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and + unpublished IMAP2bis protocols. IMAP4rev1 is largely compatible with + the IMAP4 protocol described in _R_F_C_ _1_7_3_0; the exception being in + certain facilities added in _R_F_C_ _1_7_3_0 that proved problematic and were + subsequently removed. In the course of the evolution of IMAP4rev1, + some aspects in the earlier protocols have become obsolete. Obsolete + commands, responses, and data formats which an IMAP4rev1 + implementation can encounter when used with an earlier implementation + are described in [IMAP-OBSOLETE]. + + Other compatibility issues with IMAP2bis, the most common variant of + the earlier protocol, are discussed in [IMAP-COMPAT]. A full + discussion of compatibility issues with rare (and presumed extinct) + + variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is + primarily of historical interest. + + IMAP was originally developed for the older [_R_F_C_-_8_2_2] standard, and + as a consequence several fetch items in IMAP incorporate "_R_F_C_8_2_2" in + their name. With the exception of _R_F_C_8_2_2.SIZE, there are more modern + replacements; for example, the modern version of _R_F_C_8_2_2.HEADER is + BODY.PEEK[HEADER]. In all cases, "_R_F_C_8_2_2" should be interpreted as a + reference to the updated [_R_F_C_-_2_8_2_2] standard. + +2. Protocol Overview + +2.1. Link Level + + The IMAP4rev1 protocol assumes a reliable data stream such as that + provided by TCP. When TCP is used, an IMAP4rev1 server listens on + port 143. + +2.2. Commands and Responses + + An IMAP4rev1 connection consists of the establishment of a + client/server network connection, an initial greeting from the + server, and client/server interactions. These client/server + interactions consist of a client command, server data, and a server + completion result response. + + All interactions transmitted by client and server are in the form of + lines, that is, strings that end with a CRLF. The protocol receiver + of an IMAP4rev1 client or server is either reading a line, or is + reading a sequence of octets with a known count followed by a line. + +2.2.1. Client Protocol Sender and Server Protocol Receiver + + The client command begins an operation. Each client command is + prefixed with an identifier (typically a short alphanumeric string, + e.g., A0001, A0002, etc.) called a "tag". A different tag is + generated by the client for each command. + + Clients MUST follow the syntax outlined in this specification + strictly. It is a syntax error to send a command with missing or + extraneous spaces or arguments. + + There are two cases in which a line from the client does not + represent a complete command. In one case, a command argument is + quoted with an octet count (see the description of literal in String + under Data Formats); in the other case, the command arguments require + server feedback (see the AUTHENTICATE command). In either case, the + + server sends a command continuation request response if it is ready + for the octets (if appropriate) and the remainder of the command. + This response is prefixed with the token "+". + + Note: If instead, the server detected an error in the + command, it sends a BAD completion response with a tag + matching the command (as described below) to reject the + command and prevent the client from sending any more of the + command. + + It is also possible for the server to send a completion + response for some other command (if multiple commands are + in progress), or untagged data. In either case, the + command continuation request is still pending; the client + takes the appropriate action for the response, and reads + another response from the server. In all cases, the client + MUST send a complete command (including receiving all + command continuation request responses and command + continuations for the command) before initiating a new + command. + + The protocol receiver of an IMAP4rev1 server reads a command line + from the client, parses the command and its arguments, and transmits + server data and a server command completion result response. + +2.2.2. Server Protocol Sender and Client Protocol Receiver + + Data transmitted by the server to the client and status responses + that do not indicate command completion are prefixed with the token + "*", and are called untagged responses. + + Server data MAY be sent as a result of a client command, or MAY be + sent unilaterally by the server. There is no syntactic difference + between server data that resulted from a specific command and server + data that were sent unilaterally. + + The server completion result response indicates the success or + failure of the operation. It is tagged with the same tag as the + client command which began the operation. Thus, if more than one + command is in progress, the tag in a server completion response + identifies the command to which the response applies. There are + three possible server completion responses: OK (indicating success), + NO (indicating failure), or BAD (indicating a protocol error such as + unrecognized command or command syntax error). + + Servers SHOULD enforce the syntax outlined in this specification + strictly. Any client command with a protocol syntax error, including + (but not limited to) missing or extraneous spaces or arguments, + + SHOULD be rejected, and the client given a BAD server completion + response. + + The protocol receiver of an IMAP4rev1 client reads a response line + from the server. It then takes action on the response based upon the + first token of the response, which can be a tag, a "*", or a "+". + + A client MUST be prepared to accept any server response at all times. + This includes server data that was not requested. Server data SHOULD + be recorded, so that the client can reference its recorded copy + rather than sending a command to the server to request the data. In + the case of certain server data, the data MUST be recorded. + + This topic is discussed in greater detail in the Server Responses + section. + +2.3. Message Attributes + + In addition to message text, each message has several attributes + associated with it. These attributes can be retrieved individually + or in conjunction with other attributes or message texts. + +2.3.1. Message Numbers + + Messages in IMAP4rev1 are accessed by one of two numbers; the unique + identifier or the message sequence number. + +2.3.1.1. Unique Identifier (UID) Message Attribute + + A 32-bit value assigned to each message, which when used with the + unique identifier validity value (see below) forms a 64-bit value + that MUST NOT refer to any other message in the mailbox or any + subsequent mailbox with the same name forever. Unique identifiers + are assigned in a strictly ascending fashion in the mailbox; as each + message is added to the mailbox it is assigned a higher UID than the + message(s) which were added previously. Unlike message sequence + numbers, unique identifiers are not necessarily contiguous. + + The unique identifier of a message MUST NOT change during the + session, and SHOULD NOT change between sessions. Any change of + unique identifiers between sessions MUST be detectable using the + UIDVALIDITY mechanism discussed below. Persistent unique identifiers + are required for a client to resynchronize its state from a previous + session with the server (e.g., disconnected or offline access + clients); this is discussed further in [IMAP-DISC]. + + Associated with every mailbox are two values which aid in unique + identifier handling: the next unique identifier value and the unique + identifier validity value. + + The next unique identifier value is the predicted value that will be + assigned to a new message in the mailbox. Unless the unique + identifier validity also changes (see below), the next unique + identifier value MUST have the following two characteristics. First, + the next unique identifier value MUST NOT change unless new messages + are added to the mailbox; and second, the next unique identifier + value MUST change whenever new messages are added to the mailbox, + even if those new messages are subsequently expunged. + + Note: The next unique identifier value is intended to + provide a means for a client to determine whether any + messages have been delivered to the mailbox since the + previous time it checked this value. It is not intended to + provide any guarantee that any message will have this + unique identifier. A client can only assume, at the time + that it obtains the next unique identifier value, that + messages arriving after that time will have a UID greater + than or equal to that value. + + The unique identifier validity value is sent in a UIDVALIDITY + response code in an OK untagged response at mailbox selection time. + If unique identifiers from an earlier session fail to persist in this + session, the unique identifier validity value MUST be greater than + the one used in the earlier session. + + Note: Ideally, unique identifiers SHOULD persist at all + times. Although this specification recognizes that failure + to persist can be unavoidable in certain server + environments, it STRONGLY ENCOURAGES message store + implementation techniques that avoid this problem. For + example: + + 1) Unique identifiers MUST be strictly ascending in the + mailbox at all times. If the physical message store is + re-ordered by a non-IMAP agent, this requires that the + unique identifiers in the mailbox be regenerated, since + the former unique identifiers are no longer strictly + ascending as a result of the re-ordering. + + 2) If the message store has no mechanism to store unique + identifiers, it must regenerate unique identifiers at + each session, and each session must have a unique + UIDVALIDITY value. + + 3) If the mailbox is deleted and a new mailbox with the + same name is created at a later date, the server must + either keep track of unique identifiers from the + previous instance of the mailbox, or it must assign a + new UIDVALIDITY value to the new instance of the + mailbox. A good UIDVALIDITY value to use in this case + is a 32-bit representation of the creation date/time of + the mailbox. It is alright to use a constant such as + 1, but only if it guaranteed that unique identifiers + will never be reused, even in the case of a mailbox + being deleted (or renamed) and a new mailbox by the + same name created at some future time. + + 4) The combination of mailbox name, UIDVALIDITY, and UID + must refer to a single immutable message on that server + forever. In particular, the internal date, [_R_F_C_-_2_8_2_2] + size, envelope, body structure, and message texts + (_R_F_C_8_2_2, _R_F_C_8_2_2.HEADER, _R_F_C_8_2_2.TEXT, and all BODY[...] + fetch data items) must never change. This does not + include message numbers, nor does it include attributes + that can be set by a STORE command (e.g., FLAGS). + +2.3.1.2. Message Sequence Number Message Attribute + + A relative position from 1 to the number of messages in the mailbox. + This position MUST be ordered by ascending unique identifier. As + each new message is added, it is assigned a message sequence number + that is 1 higher than the number of messages in the mailbox before + that new message was added. + + Message sequence numbers can be reassigned during the session. For + example, when a message is permanently removed (expunged) from the + mailbox, the message sequence number for all subsequent messages is + decremented. The number of messages in the mailbox is also + decremented. Similarly, a new message can be assigned a message + sequence number that was once held by some other message prior to an + expunge. + + In addition to accessing messages by relative position in the + mailbox, message sequence numbers can be used in mathematical + calculations. For example, if an untagged "11 EXISTS" is received, + and previously an untagged "8 EXISTS" was received, three new + messages have arrived with message sequence numbers of 9, 10, and 11. + Another example, if message 287 in a 523 message mailbox has UID + 12345, there are exactly 286 messages which have lesser UIDs and 236 + messages which have greater UIDs. + +2.3.2. Flags Message Attribute + + A list of zero or more named tokens associated with the message. A + flag is set by its addition to this list, and is cleared by its + removal. There are two types of flags in IMAP4rev1. A flag of + either type can be permanent or session-only. + + A system flag is a flag name that is pre-defined in this + specification. All system flags begin with "\". Certain system + flags (\Deleted and \Seen) have special semantics described + elsewhere. The currently-defined system flags are: + + \Seen + Message has been read + + \Answered + Message has been answered + + \Flagged + Message is "flagged" for urgent/special attention + + \Deleted + Message is "deleted" for removal by later EXPUNGE + + \Draft + Message has not completed composition (marked as a draft). + + \Recent + Message is "recently" arrived in this mailbox. This session + is the first session to have been notified about this + message; if the session is read-write, subsequent sessions + will not see \Recent set for this message. This flag can not + be altered by the client. + + If it is not possible to determine whether or not this + session is the first session to be notified about a message, + then that message SHOULD be considered recent. + + If multiple connections have the same mailbox selected + simultaneously, it is undefined which of these connections + will see newly-arrived messages with \Recent set and which + will see it without \Recent set. + + A keyword is defined by the server implementation. Keywords do not + begin with "\". Servers MAY permit the client to define new keywords + in the mailbox (see the description of the PERMANENTFLAGS response + code for more information). + + A flag can be permanent or session-only on a per-flag basis. + Permanent flags are those which the client can add or remove from the + message flags permanently; that is, concurrent and subsequent + sessions will see any change in permanent flags. Changes to session + flags are valid only in that session. + + Note: The \Recent system flag is a special case of a + session flag. \Recent can not be used as an argument in a + STORE or APPEND command, and thus can not be changed at + all. + +2.3.3. Internal Date Message Attribute + + The internal date and time of the message on the server. This + is not the date and time in the [_R_F_C_-_2_8_2_2] header, but rather a + date and time which reflects when the message was received. In + the case of messages delivered via [SMTP], this SHOULD be the + date and time of final delivery of the message as defined by + [SMTP]. In the case of messages delivered by the IMAP4rev1 COPY + command, this SHOULD be the internal date and time of the source + message. In the case of messages delivered by the IMAP4rev1 + APPEND command, this SHOULD be the date and time as specified in + the APPEND command description. All other cases are + implementation defined. + +2.3.4. [_R_F_C_-_2_8_2_2] Size Message Attribute + + The number of octets in the message, as expressed in [_R_F_C_-_2_8_2_2] + format. + +2.3.5. Envelope Structure Message Attribute + + A parsed representation of the [_R_F_C_-_2_8_2_2] header of the message. + Note that the IMAP Envelope structure is not the same as an + [SMTP] envelope. + +2.3.6. Body Structure Message Attribute + + A parsed representation of the [MIME-IMB] body structure + information of the message. + +2.4. Message Texts + + In addition to being able to fetch the full [_R_F_C_-_2_8_2_2] text of a + message, IMAP4rev1 permits the fetching of portions of the full + message text. Specifically, it is possible to fetch the + [_R_F_C_-_2_8_2_2] message header, [_R_F_C_-_2_8_2_2] message body, a [MIME-IMB] + body part, or a [MIME-IMB] header. + +3. State and Flow Diagram + + Once the connection between client and server is established, an + IMAP4rev1 connection is in one of four states. The initial + state is identified in the server greeting. Most commands are + only valid in certain states. It is a protocol error for the + client to attempt a command while the connection is in an + inappropriate state, and the server will respond with a BAD or + NO (depending upon server implementation) command completion + result. + +3.1. Not Authenticated State + + In the not authenticated state, the client MUST supply + authentication credentials before most commands will be + permitted. This state is entered when a connection starts + unless the connection has been pre-authenticated. + +3.2. Authenticated State + + In the authenticated state, the client is authenticated and MUST + select a mailbox to access before commands that affect messages + will be permitted. This state is entered when a + pre-authenticated connection starts, when acceptable + authentication credentials have been provided, after an error in + selecting a mailbox, or after a successful CLOSE command. + +3.3. Selected State + + In a selected state, a mailbox has been selected to access. + This state is entered when a mailbox has been successfully + selected. + +3.4. Logout State + + In the logout state, the connection is being terminated. This + state can be entered as a result of a client request (via the + LOGOUT command) or by unilateral action on the part of either + the client or server. + + If the client requests the logout state, the server MUST send an + untagged BYE response and a tagged OK response to the LOGOUT + command before the server closes the connection; and the client + MUST read the tagged OK response to the LOGOUT command before + the client closes the connection. + + A server MUST NOT unilaterally close the connection without + sending an untagged BYE response that contains the reason for + having done so. A client SHOULD NOT unilaterally close the + connection, and instead SHOULD issue a LOGOUT command. If the + server detects that the client has unilaterally closed the + connection, the server MAY omit the untagged BYE response and + simply close its connection. + + +----------------------+ + |connection established| + +----------------------+ + || + \/ + +--------------------------------------+ + | server greeting | + +--------------------------------------+ + || (1) || (2) || (3) + \/ || || + +-----------------+ || || + |Not Authenticated| || || + +-----------------+ || || + || (7) || (4) || || + || \/ \/ || + || +----------------+ || + || | Authenticated |<=++ || + || +----------------+ || || + || || (7) || (5) || (6) || + || || \/ || || + || || +--------+ || || + || || |Selected|==++ || + || || +--------+ || + || || || (7) || + \/ \/ \/ \/ + +--------------------------------------+ + | Logout | + +--------------------------------------+ + || + \/ + +-------------------------------+ + |both sides close the connection| + +-------------------------------+ + + (1) connection without pre-authentication (OK greeting) + (2) pre-authenticated connection (PREAUTH greeting) + (3) rejected connection (BYE greeting) + (4) successful LOGIN or AUTHENTICATE command + (5) successful SELECT or EXAMINE command + (6) CLOSE command, or failed SELECT or EXAMINE command + (7) LOGOUT command, server shutdown, or connection closed + +4. Data Formats + + IMAP4rev1 uses textual commands and responses. Data in + IMAP4rev1 can be in one of several forms: atom, number, string, + parenthesized list, or NIL. Note that a particular data item + may take more than one form; for example, a data item defined as + using "astring" syntax may be either an atom or a string. + +4.1. Atom + + An atom consists of one or more non-special characters. + +4.2. Number + + A number consists of one or more digit characters, and + represents a numeric value. + +4.3. String + + A string is in one of two forms: either literal or quoted + string. The literal form is the general form of string. The + quoted string form is an alternative that avoids the overhead of + processing a literal at the cost of limitations of characters + which may be used. + + A literal is a sequence of zero or more octets (including CR and + LF), prefix-quoted with an octet count in the form of an open + brace ("{"), the number of octets, close brace ("}"), and CRLF. + In the case of literals transmitted from server to client, the + CRLF is immediately followed by the octet data. In the case of + literals transmitted from client to server, the client MUST wait + to receive a command continuation request (described later in + this document) before sending the octet data (and the remainder + of the command). + + A quoted string is a sequence of zero or more 7-bit characters, + excluding CR and LF, with double quote (<">) characters at each + end. + + The empty string is represented as either "" (a quoted string + with zero characters between double quotes) or as {0} followed + by CRLF (a literal with an octet count of 0). + + Note: Even if the octet count is 0, a client transmitting a + literal MUST wait to receive a command continuation request. + +4.3.1. 8-bit and Binary Strings + + 8-bit textual and binary mail is supported through the use of a + [MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY + transmit 8-bit or multi-octet characters in literals, but SHOULD do + so only when the [CHARSET] is identified. + + Although a BINARY body encoding is defined, unencoded binary strings + are not permitted. A "binary string" is any string with NUL + characters. Implementations MUST encode binary data into a textual + form, such as BASE64, before transmitting the data. A string with an + excessive amount of CTL characters MAY also be considered to be + binary. + +4.4. Parenthesized List + + Data structures are represented as a "parenthesized list"; a sequence + of data items, delimited by space, and bounded at each end by + parentheses. A parenthesized list can contain other parenthesized + lists, using multiple levels of parentheses to indicate nesting. + + The empty list is represented as () -- a parenthesized list with no + members. + +4.5. NIL + + The special form "NIL" represents the non-existence of a particular + data item that is represented as a string or parenthesized list, as + distinct from the empty string "" or the empty parenthesized list (). + + Note: NIL is never used for any data item which takes the + form of an atom. For example, a mailbox name of "NIL" is a + mailbox named NIL as opposed to a non-existent mailbox + name. This is because mailbox uses "astring" syntax which + is an atom or a string. Conversely, an addr-name of NIL is + a non-existent personal name, because addr-name uses + "nstring" syntax which is NIL or a string, but never an + atom. + +5. Operational Considerations + + The following rules are listed here to ensure that all IMAP4rev1 + implementations interoperate properly. + +5.1. Mailbox Naming + + Mailbox names are 7-bit. Client implementations MUST NOT attempt to + create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox + names returned by LIST or LSUB as UTF-8. Server implementations + SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT + return 8-bit mailbox names in LIST or LSUB. See section 5.1.3 for + more information on how to represent non-ASCII mailbox names. + + Note: 8-bit mailbox names were undefined in earlier + versions of this protocol. Some sites used a local 8-bit + character set to represent non-ASCII mailbox names. Such + usage is not interoperable, and is now formally deprecated. + + The case-insensitive mailbox name INBOX is a special name reserved to + mean "the primary mailbox for this user on this server". The + interpretation of all other names is implementation-dependent. + + In particular, this specification takes no position on case + sensitivity in non-INBOX mailbox names. Some server implementations + are fully case-sensitive; others preserve case of a newly-created + name but otherwise are case-insensitive; and yet others coerce names + to a particular case. Client implementations MUST interact with any + of these. If a server implementation interprets non-INBOX mailbox + names as case-insensitive, it MUST treat names using the + international naming convention specially as described in section + 5.1.3. + + There are certain client considerations when creating a new mailbox + name: + + 1) Any character which is one of the atom-specials (see the Formal + Syntax) will require that the mailbox name be represented as a + quoted string or literal. + + 2) CTL and other non-graphic characters are difficult to represent + in a user interface and are best avoided. + + 3) Although the list-wildcard characters ("%" and "*") are valid + in a mailbox name, it is difficult to use such mailbox names + with the LIST and LSUB commands due to the conflict with + wildcard interpretation. + + 4) Usually, a character (determined by the server implementation) + is reserved to delimit levels of hierarchy. + + 5) Two characters, "#" and "&", have meanings by convention, and + should be avoided except when used in that convention. + +5.1.1. Mailbox Hierarchy Naming + + If it is desired to export hierarchical mailbox names, mailbox names + MUST be left-to-right hierarchical using a single character to + separate levels of hierarchy. The same hierarchy separator character + is used for all levels of hierarchy within a single name. + +5.1.2. Mailbox Namespace Naming Convention + + By convention, the first hierarchical element of any mailbox name + which begins with "#" identifies the "namespace" of the remainder of + the name. This makes it possible to disambiguate between different + types of mailbox stores, each of which have their own namespaces. + + For example, implementations which offer access to USENET + newsgroups MAY use the "#news" namespace to partition the + USENET newsgroup namespace from that of other mailboxes. + Thus, the comp.mail.misc newsgroup would have a mailbox + name of "#news.comp.mail.misc", and the name + "comp.mail.misc" can refer to a different object (e.g., a + user's private mailbox). + +5.1.3. Mailbox International Naming Convention + + By convention, international mailbox names in IMAP4rev1 are specified + using a modified version of the UTF-7 encoding described in [UTF-7]. + Modified UTF-7 may also be usable in servers that implement an + earlier version of this protocol. + + In modified UTF-7, printable US-ASCII characters, except for "&", + represent themselves; that is, characters with octet values 0x20-0x25 + and 0x27-0x7e. The character "&" (0x26) is represented by the + two-octet sequence "&-". + + All other characters (octet values 0x00-0x1f and 0x7f-0xff) are + represented in modified BASE64, with a further modification from + [UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be + used to represent any printing US-ASCII character which can represent + itself. + + "&" is used to shift to modified BASE64 and "-" to shift back to + US-ASCII. There is no implicit shift from BASE64 to US-ASCII, and + null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII + means "&") are not permitted. However, all names start in US-ASCII, + and MUST end in US-ASCII; that is, a name that ends with a non-ASCII + ISO-10646 character MUST end with a "-"). + + The purpose of these modifications is to correct the following + problems with UTF-7: + + 1) UTF-7 uses the "+" character for shifting; this conflicts with + the common use of "+" in mailbox names, in particular USENET + newsgroup names. + + 2) UTF-7's encoding is BASE64 which uses the "/" character; this + conflicts with the use of "/" as a popular hierarchy delimiter. + + 3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with + the use of "\" as a popular hierarchy delimiter. + + 4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with + the use of "~" in some servers as a home directory indicator. + + 5) UTF-7 permits multiple alternate forms to represent the same + string; in particular, printable US-ASCII characters can be + represented in encoded form. + + Although modified UTF-7 is a convention, it establishes certain + requirements on server handling of any mailbox name with an + embedded "&" character. In particular, server implementations + MUST preserve the exact form of the modified BASE64 portion of a + modified UTF-7 name and treat that text as case-sensitive, even if + names are otherwise case-insensitive or case-folded. + + Server implementations SHOULD verify that any mailbox name with an + embedded "&" character, used as an argument to CREATE, is: in the + correctly modified UTF-7 syntax, has no superfluous shifts, and + has no encoding in modified BASE64 of any printing US-ASCII + character which can represent itself. However, client + implementations MUST NOT depend upon the server doing this, and + SHOULD NOT attempt to create a mailbox name with an embedded "&" + character unless it complies with the modified UTF-7 syntax. + + Server implementations which export a mail store that does not + follow the modified UTF-7 convention MUST convert to modified + UTF-7 any mailbox name that contains either non-ASCII characters + or the "&" character. + + For example, here is a mailbox name which mixes English, + Chinese, and Japanese text: + ~peter/mail/&U,BTFw-/&ZeVnLIqe- + + For example, the string "&Jjo!" is not a valid mailbox + name because it does not contain a shift to US-ASCII + before the "!". The correct form is "&Jjo-!". The + string "&U,BTFw-&ZeVnLIqe-" is not permitted because it + contains a superfluous shift. The correct form is + "&U,BTF2XlZyyKng-". + +5.2. Mailbox Size and Message Status Updates + + At any time, a server can send data that the client did not request. + Sometimes, such behavior is REQUIRED. For example, agents other than + the server MAY add messages to the mailbox (e.g., new message + delivery), change the flags of the messages in the mailbox (e.g., + simultaneous access to the same mailbox by multiple agents), or even + remove messages from the mailbox. A server MUST send mailbox size + updates automatically if a mailbox size change is observed during the + processing of a command. A server SHOULD send message flag updates + automatically, without requiring the client to request such updates + explicitly. + + Special rules exist for server notification of a client about the + removal of messages to prevent synchronization errors; see the + description of the EXPUNGE response for more detail. In particular, + it is NOT permitted to send an EXISTS response that would reduce the + number of messages in the mailbox; only the EXPUNGE response can do + this. + + Regardless of what implementation decisions a client makes on + remembering data from the server, a client implementation MUST record + mailbox size updates. It MUST NOT assume that any command after the + initial mailbox selection will return the size of the mailbox. + +5.3. Response when no Command in Progress + + Server implementations are permitted to send an untagged response + (except for EXPUNGE) while there is no command in progress. Server + implementations that send such responses MUST deal with flow control + considerations. Specifically, they MUST either (1) verify that the + size of the data does not exceed the underlying transport's available + window size, or (2) use non-blocking writes. + +5.4. Autologout Timer + + If a server has an inactivity autologout timer, the duration of that + timer MUST be at least 30 minutes. The receipt of ANY command from + the client during that interval SHOULD suffice to reset the + autologout timer. + +5.5. Multiple Commands in Progress + + The client MAY send another command without waiting for the + completion result response of a command, subject to ambiguity rules + (see below) and flow control constraints on the underlying data + stream. Similarly, a server MAY begin processing another command + before processing the current command to completion, subject to + ambiguity rules. However, any command continuation request responses + and command continuations MUST be negotiated before any subsequent + command is initiated. + + The exception is if an ambiguity would result because of a command + that would affect the results of other commands. Clients MUST NOT + send multiple commands without waiting if an ambiguity would result. + If the server detects a possible ambiguity, it MUST execute commands + to completion in the order given by the client. + + The most obvious example of ambiguity is when a command would affect + the results of another command, e.g., a FETCH of a message's flags + and a STORE of that same message's flags. + + A non-obvious ambiguity occurs with commands that permit an untagged + EXPUNGE response (commands other than FETCH, STORE, and SEARCH), + since an untagged EXPUNGE response can invalidate sequence numbers in + a subsequent command. This is not a problem for FETCH, STORE, or + SEARCH commands because servers are prohibited from sending EXPUNGE + responses while any of those commands are in progress. Therefore, if + the client sends any command other than FETCH, STORE, or SEARCH, it + MUST wait for the completion result response before sending a command + with message sequence numbers. + + Note: UID FETCH, UID STORE, and UID SEARCH are different + commands from FETCH, STORE, and SEARCH. If the client + sends a UID command, it must wait for a completion result + response before sending a command with message sequence + numbers. + + For example, the following non-waiting command sequences are invalid: + + FETCH + NOOP + STORE + STORE + COPY + FETCH + COPY + COPY + CHECK + FETCH + + The following are examples of valid non-waiting command sequences: + + FETCH + STORE + SEARCH + CHECK + STORE + COPY + EXPUNGE + + UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting + command sequence, depending upon whether or not the second UID + SEARCH contains message sequence numbers. + +6. Client Commands + + IMAP4rev1 commands are described in this section. Commands are + organized by the state in which the command is permitted. Commands + which are permitted in multiple states are listed in the minimum + permitted state (for example, commands valid in authenticated and + selected state are listed in the authenticated state commands). + + Command arguments, identified by "Arguments:" in the command + descriptions below, are described by function, not by syntax. The + precise syntax of command arguments is described in the Formal Syntax + section. + + Some commands cause specific server responses to be returned; these + are identified by "Responses:" in the command descriptions below. + See the response descriptions in the Responses section for + information on these responses, and the Formal Syntax section for the + precise syntax of these responses. It is possible for server data to + be transmitted as a result of any command. Thus, commands that do + not specifically require server data specify "no specific responses + for this command" instead of "none". + + The "Result:" in the command description refers to the possible + tagged status responses to a command, and any special interpretation + of these status responses. + + The state of a connection is only changed by successful commands + which are documented as changing state. A rejected command (BAD + response) never changes the state of the connection or of the + selected mailbox. A failed command (NO response) generally does not + change the state of the connection or of the selected mailbox; the + exception being the SELECT and EXAMINE commands. + +6.1. Client Commands - Any State + + The following commands are valid in any state: CAPABILITY, NOOP, and + LOGOUT. + +6.1.1. CAPABILITY Command + + Arguments: none + + Responses: REQUIRED untagged response: CAPABILITY + + Result: OK - capability completed + BAD - command unknown or arguments invalid + + The CAPABILITY command requests a listing of capabilities that the + server supports. The server MUST send a single untagged + CAPABILITY response with "IMAP4rev1" as one of the listed + capabilities before the (tagged) OK response. + + A capability name which begins with "AUTH=" indicates that the + server supports that particular authentication mechanism. All + such names are, by definition, part of this specification. For + example, the authorization capability for an experimental + "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not + "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP". + + Other capability names refer to extensions, revisions, or + amendments to this specification. See the documentation of the + CAPABILITY response for additional information. No capabilities, + beyond the base IMAP4rev1 set defined in this specification, are + enabled without explicit client action to invoke the capability. + + Client and server implementations MUST implement the STARTTLS, + LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS]) + capabilities. See the Security Considerations section for + important information. + + See the section entitled "Client Commands - + Experimental/Expansion" for information about the form of site or + implementation-specific capabilities. + + Example: C: abcd CAPABILITY + S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI + LOGINDISABLED + S: abcd OK CAPABILITY completed + C: efgh STARTTLS + S: efgh OK STARTLS completed + <TLS negotiation, further commands are under [TLS] layer> + C: ijkl CAPABILITY + S: * CAPABILITY IMAP4rev1 AUTH=GSSAPI AUTH=PLAIN + S: ijkl OK CAPABILITY completed + +6.1.2. NOOP Command + + Arguments: none + + Responses: no specific responses for this command (but see below) + + Result: OK - noop completed + BAD - command unknown or arguments invalid + + The NOOP command always succeeds. It does nothing. + + Since any command can return a status update as untagged data, the + NOOP command can be used as a periodic poll for new messages or + message status updates during a period of inactivity (this is the + preferred method to do this). The NOOP command can also be used + to reset any inactivity autologout timer on the server. + + Example: C: a002 NOOP + S: a002 OK NOOP completed + . . . + C: a047 NOOP + S: * 22 EXPUNGE + S: * 23 EXISTS + S: * 3 RECENT + S: * 14 FETCH (FLAGS (\Seen \Deleted)) + S: a047 OK NOOP completed + +6.1.3. LOGOUT Command + + Arguments: none + + Responses: REQUIRED untagged response: BYE + + Result: OK - logout completed + BAD - command unknown or arguments invalid + + The LOGOUT command informs the server that the client is done with + the connection. The server MUST send a BYE untagged response + before the (tagged) OK response, and then close the network + connection. + + Example: C: A023 LOGOUT + S: * BYE IMAP4rev1 Server logging out + S: A023 OK LOGOUT completed + (Server and client then close the connection) + +6.2. Client Commands - Not Authenticated State + + In the not authenticated state, the AUTHENTICATE or LOGIN command + establishes authentication and enters the authenticated state. The + AUTHENTICATE command provides a general mechanism for a variety of + authentication techniques, privacy protection, and integrity + checking; whereas the LOGIN command uses a traditional user name and + plaintext password pair and has no means of establishing privacy + protection or integrity checking. + + The STARTTLS command is an alternate form of establishing session + privacy protection and integrity checking, but does not establish + authentication or enter the authenticated state. + + Server implementations MAY allow access to certain mailboxes without + establishing authentication. This can be done by means of the + ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older + convention is a LOGIN command using the userid "anonymous"; in this + case, a password is required although the server may choose to accept + any password. The restrictions placed on anonymous users are + implementation-dependent. + + Once authenticated (including as anonymous), it is not possible to + re-enter not authenticated state. + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + the following commands are valid in the not authenticated state: + STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations + section for important information about these commands. + +6.2.1. STARTTLS Command + + Arguments: none + + Responses: no specific response for this command + + Result: OK - starttls completed, begin TLS negotiation + BAD - command unknown or arguments invalid + + A [TLS] negotiation begins immediately after the CRLF at the end + of the tagged OK response from the server. Once a client issues a + STARTTLS command, it MUST NOT issue further commands until a + server response is seen and the [TLS] negotiation is complete. + + The server remains in the non-authenticated state, even if client + credentials are supplied during the [TLS] negotiation. This does + not preclude an authentication mechanism such as EXTERNAL (defined + in [SASL]) from using client identity determined by the [TLS] + negotiation. + + Once [TLS] has been started, the client MUST discard cached + information about server capabilities and SHOULD re-issue the + CAPABILITY command. This is necessary to protect against man-in- + the-middle attacks which alter the capabilities list prior to + STARTTLS. The server MAY advertise different capabilities after + STARTTLS. + + Example: C: a001 CAPABILITY + S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED + S: a001 OK CAPABILITY completed + C: a002 STARTTLS + S: a002 OK Begin TLS negotiation now + <TLS negotiation, further commands are under [TLS] layer> + C: a003 CAPABILITY + S: * CAPABILITY IMAP4rev1 AUTH=PLAIN + S: a003 OK CAPABILITY completed + C: a004 LOGIN joe password + S: a004 OK LOGIN completed + +6.2.2. AUTHENTICATE Command + + Arguments: authentication mechanism name + + Responses: continuation data can be requested + + Result: OK - authenticate completed, now in authenticated state + NO - authenticate failure: unsupported authentication + mechanism, credentials rejected + BAD - command unknown or arguments invalid, + authentication exchange cancelled + + The AUTHENTICATE command indicates a [SASL] authentication + mechanism to the server. If the server supports the requested + authentication mechanism, it performs an authentication protocol + exchange to authenticate and identify the client. It MAY also + negotiate an OPTIONAL security layer for subsequent protocol + interactions. If the requested authentication mechanism is not + supported, the server SHOULD reject the AUTHENTICATE command by + sending a tagged NO response. + + The AUTHENTICATE command does not support the optional "initial + response" feature of [SASL]. Section 5.1 of [SASL] specifies how + to handle an authentication mechanism which uses an initial + response. + + The service name specified by this protocol's profile of [SASL] is + "imap". + + The authentication protocol exchange consists of a series of + server challenges and client responses that are specific to the + authentication mechanism. A server challenge consists of a + command continuation request response with the "+" token followed + by a BASE64 encoded string. The client response consists of a + single line consisting of a BASE64 encoded string. If the client + wishes to cancel an authentication exchange, it issues a line + consisting of a single "*". If the server receives such a + response, it MUST reject the AUTHENTICATE command by sending a + tagged BAD response. + + If a security layer is negotiated through the [SASL] + authentication exchange, it takes effect immediately following the + CRLF that concludes the authentication exchange for the client, + and the CRLF of the tagged OK response for the server. + + While client and server implementations MUST implement the + AUTHENTICATE command itself, it is not required to implement any + authentication mechanisms other than the PLAIN mechanism described + + in [IMAP-TLS]. Also, an authentication mechanism is not required + to support any security layers. + + Note: a server implementation MUST implement a + configuration in which it does NOT permit any plaintext + password mechanisms, unless either the STARTTLS command + has been negotiated or some other mechanism that + protects the session from password snooping has been + provided. Server sites SHOULD NOT use any configuration + which permits a plaintext password mechanism without + such a protection mechanism against password snooping. + Client and server implementations SHOULD implement + additional [SASL] mechanisms that do not use plaintext + passwords, such the GSSAPI mechanism described in [SASL] + and/or the [DIGEST-MD5] mechanism. + + Servers and clients can support multiple authentication + mechanisms. The server SHOULD list its supported authentication + mechanisms in the response to the CAPABILITY command so that the + client knows which authentication mechanisms to use. + + A server MAY include a CAPABILITY response code in the tagged OK + response of a successful AUTHENTICATE command in order to send + capabilities automatically. It is unnecessary for a client to + send a separate CAPABILITY command if it recognizes these + automatic capabilities. This should only be done if a security + layer was not negotiated by the AUTHENTICATE command, because the + tagged OK response as part of an AUTHENTICATE command is not + protected by encryption/integrity checking. [SASL] requires the + client to re-issue a CAPABILITY command in this case. + + If an AUTHENTICATE command fails with a NO response, the client + MAY try another authentication mechanism by issuing another + AUTHENTICATE command. It MAY also attempt to authenticate by + using the LOGIN command (see section 6.2.3 for more detail). In + other words, the client MAY request authentication types in + decreasing order of preference, with the LOGIN command as a last + resort. + + The authorization identity passed from the client to the server + during the authentication exchange is interpreted by the server as + the user name whose privileges the client is requesting. + + Example: S: * OK IMAP4rev1 Server + C: A001 AUTHENTICATE GSSAPI + S: + + C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw + MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0 + b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW + Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA + cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX + AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y + C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb + I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi + vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL + pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n + FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE + NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx + O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB + vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg== + S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC + AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0 + uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg== + C: + S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe + ceP2CWY0SR0fAQAgAAQEBAQ= + C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP + wkhbfa2QteAQAgAG1yYwE= + S: A001 OK GSSAPI authentication successful + + Note: The line breaks within server challenges and client + responses are for editorial clarity and are not in real + authenticators. + +6.2.3. LOGIN Command + + Arguments: user name + password + + Responses: no specific responses for this command + + Result: OK - login completed, now in authenticated state + NO - login failure: user name or password rejected + BAD - command unknown or arguments invalid + + The LOGIN command identifies the client to the server and carries + the plaintext password authenticating this user. + + A server MAY include a CAPABILITY response code in the tagged OK + response to a successful LOGIN command in order to send + capabilities automatically. It is unnecessary for a client to + send a separate CAPABILITY command if it recognizes these + automatic capabilities. + + Example: C: a001 LOGIN SMITH SESAME + S: a001 OK LOGIN completed + + Note: Use of the LOGIN command over an insecure network + (such as the Internet) is a security risk, because anyone + monitoring network traffic can obtain plaintext passwords. + The LOGIN command SHOULD NOT be used except as a last + resort, and it is recommended that client implementations + have a means to disable any automatic use of the LOGIN + command. + + Unless either the STARTTLS command has been negotiated or + some other mechanism that protects the session from + password snooping has been provided, a server + implementation MUST implement a configuration in which it + advertises the LOGINDISABLED capability and does NOT permit + the LOGIN command. Server sites SHOULD NOT use any + configuration which permits the LOGIN command without such + a protection mechanism against password snooping. A client + implementation MUST NOT send a LOGIN command if the + LOGINDISABLED capability is advertised. + +6.3. Client Commands - Authenticated State + + In the authenticated state, commands that manipulate mailboxes as + atomic entities are permitted. Of these commands, the SELECT and + EXAMINE commands will select a mailbox for access and enter the + selected state. + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + the following commands are valid in the authenticated state: SELECT, + EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, + STATUS, and APPEND. + +6.3.1. SELECT Command + + Arguments: mailbox name + + Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT + REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS, + UIDNEXT, UIDVALIDITY + + Result: OK - select completed, now in selected state + NO - select failure, now in authenticated state: no + such mailbox, can't access mailbox + BAD - command unknown or arguments invalid + + The SELECT command selects a mailbox so that messages in the + mailbox can be accessed. Before returning an OK to the client, + the server MUST send the following untagged data to the client. + Note that earlier versions of this protocol only required the + FLAGS, EXISTS, and RECENT untagged data; consequently, client + implementations SHOULD implement default behavior for missing data + as discussed with the individual item. + + FLAGS Defined flags in the mailbox. See the description + of the FLAGS response for more detail. + + <n> EXISTS The number of messages in the mailbox. See the + description of the EXISTS response for more detail. + + <n> RECENT The number of messages with the \Recent flag set. + See the description of the RECENT response for more + detail. + + OK [UNSEEN <n>] + The message sequence number of the first unseen + message in the mailbox. If this is missing, the + client can not make any assumptions about the first + unseen message in the mailbox, and needs to issue a + SEARCH command if it wants to find it. + + OK [PERMANENTFLAGS (<list of flags>)] + A list of message flags that the client can change + permanently. If this is missing, the client should + assume that all flags can be changed permanently. + + OK [UIDNEXT <n>] + The next unique identifier value. Refer to section + 2.3.1.1 for more information. If this is missing, + the client can not make any assumptions about the + next unique identifier value. + + OK [UIDVALIDITY <n>] + The unique identifier validity value. Refer to + section 2.3.1.1 for more information. If this is + missing, the server does not support unique + identifiers. + + Only one mailbox can be selected at a time in a connection; + simultaneous access to multiple mailboxes requires multiple + connections. The SELECT command automatically deselects any + currently selected mailbox before attempting the new selection. + Consequently, if a mailbox is selected and a SELECT command that + fails is attempted, no mailbox is selected. + + If the client is permitted to modify the mailbox, the server + SHOULD prefix the text of the tagged OK response with the + "[READ-WRITE]" response code. + + If the client is not permitted to modify the mailbox but is + permitted read access, the mailbox is selected as read-only, and + the server MUST prefix the text of the tagged OK response to + SELECT with the "[READ-ONLY]" response code. Read-only access + through SELECT differs from the EXAMINE command in that certain + read-only mailboxes MAY permit the change of permanent state on a + per-user (as opposed to global) basis. Netnews messages marked in + a server-based .newsrc file are an example of such per-user + permanent state that can be modified with read-only mailboxes. + + Example: C: A142 SELECT INBOX + S: * 172 EXISTS + S: * 1 RECENT + S: * OK [UNSEEN 12] Message 12 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited + S: A142 OK [READ-WRITE] SELECT completed + +6.3.2. EXAMINE Command + + Arguments: mailbox name + + Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT + REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS, + UIDNEXT, UIDVALIDITY + + Result: OK - examine completed, now in selected state + NO - examine failure, now in authenticated state: no + such mailbox, can't access mailbox + BAD - command unknown or arguments invalid + + The EXAMINE command is identical to SELECT and returns the same + output; however, the selected mailbox is identified as read-only. + No changes to the permanent state of the mailbox, including + per-user state, are permitted; in particular, EXAMINE MUST NOT + cause messages to lose the \Recent flag. + + The text of the tagged OK response to the EXAMINE command MUST + begin with the "[READ-ONLY]" response code. + + Example: C: A932 EXAMINE blurdybloop + S: * 17 EXISTS + S: * 2 RECENT + S: * OK [UNSEEN 8] Message 8 is first unseen + S: * OK [UIDVALIDITY 3857529045] UIDs valid + S: * OK [UIDNEXT 4392] Predicted next UID + S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + S: * OK [PERMANENTFLAGS ()] No permanent flags permitted + S: A932 OK [READ-ONLY] EXAMINE completed + +6.3.3. CREATE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - create completed + NO - create failure: can't create mailbox with that name + BAD - command unknown or arguments invalid + + The CREATE command creates a mailbox with the given name. An OK + response is returned only if a new mailbox with that name has been + created. It is an error to attempt to create INBOX or a mailbox + with a name that refers to an extant mailbox. Any error in + creation will return a tagged NO response. + + If the mailbox name is suffixed with the server's hierarchy + separator character (as returned from the server by a LIST + command), this is a declaration that the client intends to create + mailbox names under this name in the hierarchy. Server + implementations that do not require this declaration MUST ignore + the declaration. In any case, the name created is without the + trailing hierarchy delimiter. + + If the server's hierarchy separator character appears elsewhere in + the name, the server SHOULD create any superior hierarchical names + that are needed for the CREATE command to be successfully + completed. In other words, an attempt to create "foo/bar/zap" on + a server in which "/" is the hierarchy separator character SHOULD + create foo/ and foo/bar/ if they do not already exist. + + If a new mailbox is created with the same name as a mailbox which + was deleted, its unique identifiers MUST be greater than any + unique identifiers used in the previous incarnation of the mailbox + UNLESS the new incarnation has a different unique identifier + validity value. See the description of the UID command for more + detail. + + Example: C: A003 CREATE owatagusiam/ + S: A003 OK CREATE completed + C: A004 CREATE owatagusiam/blurdybloop + S: A004 OK CREATE completed + + Note: The interpretation of this example depends on whether + "/" was returned as the hierarchy separator from LIST. If + "/" is the hierarchy separator, a new level of hierarchy + named "owatagusiam" with a member called "blurdybloop" is + created. Otherwise, two mailboxes at the same hierarchy + level are created. + +6.3.4. DELETE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - delete completed + NO - delete failure: can't delete mailbox with that name + BAD - command unknown or arguments invalid + + The DELETE command permanently removes the mailbox with the given + name. A tagged OK response is returned only if the mailbox has + been deleted. It is an error to attempt to delete INBOX or a + mailbox name that does not exist. + + The DELETE command MUST NOT remove inferior hierarchical names. + For example, if a mailbox "foo" has an inferior "foo.bar" + (assuming "." is the hierarchy delimiter character), removing + "foo" MUST NOT remove "foo.bar". It is an error to attempt to + delete a name that has inferior hierarchical names and also has + the \Noselect mailbox name attribute (see the description of the + LIST response for more details). + + It is permitted to delete a name that has inferior hierarchical + names and does not have the \Noselect mailbox name attribute. In + this case, all messages in that mailbox are removed, and the name + will acquire the \Noselect mailbox name attribute. + + The value of the highest-used unique identifier of the deleted + mailbox MUST be preserved so that a new mailbox created with the + same name will not reuse the identifiers of the former + incarnation, UNLESS the new incarnation has a different unique + identifier validity value. See the description of the UID command + for more detail. + + Examples: C: A682 LIST "" * + S: * LIST () "/" blurdybloop + S: * LIST (\Noselect) "/" foo + S: * LIST () "/" foo/bar + S: A682 OK LIST completed + C: A683 DELETE blurdybloop + S: A683 OK DELETE completed + C: A684 DELETE foo + S: A684 NO Name "foo" has inferior hierarchical names + C: A685 DELETE foo/bar + S: A685 OK DELETE Completed + C: A686 LIST "" * + S: * LIST (\Noselect) "/" foo + S: A686 OK LIST completed + C: A687 DELETE foo + S: A687 OK DELETE Completed + + C: A82 LIST "" * + S: * LIST () "." blurdybloop + S: * LIST () "." foo + S: * LIST () "." foo.bar + S: A82 OK LIST completed + C: A83 DELETE blurdybloop + S: A83 OK DELETE completed + C: A84 DELETE foo + S: A84 OK DELETE Completed + C: A85 LIST "" * + S: * LIST () "." foo.bar + S: A85 OK LIST completed + C: A86 LIST "" % + S: * LIST (\Noselect) "." foo + S: A86 OK LIST completed + +6.3.5. RENAME Command + + Arguments: existing mailbox name + new mailbox name + + Responses: no specific responses for this command + + Result: OK - rename completed + NO - rename failure: can't rename mailbox with that name, + can't rename to mailbox with that name + BAD - command unknown or arguments invalid + + The RENAME command changes the name of a mailbox. A tagged OK + response is returned only if the mailbox has been renamed. It is + an error to attempt to rename from a mailbox name that does not + exist or to a mailbox name that already exists. Any error in + renaming will return a tagged NO response. + + If the name has inferior hierarchical names, then the inferior + hierarchical names MUST also be renamed. For example, a rename of + "foo" to "zap" will rename "foo/bar" (assuming "/" is the + hierarchy delimiter character) to "zap/bar". + + If the server's hierarchy separator character appears in the name, + the server SHOULD create any superior hierarchical names that are + needed for the RENAME command to complete successfully. In other + words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a + server in which "/" is the hierarchy separator character SHOULD + create baz/ and baz/rag/ if they do not already exist. + + The value of the highest-used unique identifier of the old mailbox + name MUST be preserved so that a new mailbox created with the same + name will not reuse the identifiers of the former incarnation, + UNLESS the new incarnation has a different unique identifier + validity value. See the description of the UID command for more + detail. + + Renaming INBOX is permitted, and has special behavior. It moves + all messages in INBOX to a new mailbox with the given name, + leaving INBOX empty. If the server implementation supports + inferior hierarchical names of INBOX, these are unaffected by a + rename of INBOX. + + Examples: C: A682 LIST "" * + S: * LIST () "/" blurdybloop + S: * LIST (\Noselect) "/" foo + S: * LIST () "/" foo/bar + S: A682 OK LIST completed + C: A683 RENAME blurdybloop sarasoop + S: A683 OK RENAME completed + C: A684 RENAME foo zowie + S: A684 OK RENAME Completed + C: A685 LIST "" * + S: * LIST () "/" sarasoop + S: * LIST (\Noselect) "/" zowie + S: * LIST () "/" zowie/bar + S: A685 OK LIST completed + + C: Z432 LIST "" * + S: * LIST () "." INBOX + S: * LIST () "." INBOX.bar + S: Z432 OK LIST completed + C: Z433 RENAME INBOX old-mail + S: Z433 OK RENAME completed + C: Z434 LIST "" * + S: * LIST () "." INBOX + S: * LIST () "." INBOX.bar + S: * LIST () "." old-mail + S: Z434 OK LIST completed + +6.3.6. SUBSCRIBE Command + + Arguments: mailbox + + Responses: no specific responses for this command + + Result: OK - subscribe completed + NO - subscribe failure: can't subscribe to that name + BAD - command unknown or arguments invalid + + The SUBSCRIBE command adds the specified mailbox name to the + server's set of "active" or "subscribed" mailboxes as returned by + the LSUB command. This command returns a tagged OK response only + if the subscription is successful. + + A server MAY validate the mailbox argument to SUBSCRIBE to verify + that it exists. However, it MUST NOT unilaterally remove an + existing mailbox name from the subscription list even if a mailbox + by that name no longer exists. + + Note: This requirement is because a server site can + choose to routinely remove a mailbox with a well-known + name (e.g., "system-alerts") after its contents expire, + with the intention of recreating it when new contents + are appropriate. + + Example: C: A002 SUBSCRIBE #news.comp.mail.mime + S: A002 OK SUBSCRIBE completed + +6.3.7. UNSUBSCRIBE Command + + Arguments: mailbox name + + Responses: no specific responses for this command + + Result: OK - unsubscribe completed + NO - unsubscribe failure: can't unsubscribe that name + BAD - command unknown or arguments invalid + + The UNSUBSCRIBE command removes the specified mailbox name from + the server's set of "active" or "subscribed" mailboxes as returned + by the LSUB command. This command returns a tagged OK response + only if the unsubscription is successful. + + Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime + S: A002 OK UNSUBSCRIBE completed + +6.3.8. LIST Command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LIST + + Result: OK - list completed + NO - list failure: can't list that reference or name + BAD - command unknown or arguments invalid + + The LIST command returns a subset of names from the complete set + of all names available to the client. Zero or more untagged LIST + replies are returned, containing the name attributes, hierarchy + delimiter, and name; see the description of the LIST reply for + more detail. + + The LIST command SHOULD return its data quickly, without undue + delay. For example, it SHOULD NOT go to excess trouble to + calculate the \Marked or \Unmarked status or perform other + processing; if each name requires 1 second of processing, then a + list of 1200 names would take 20 minutes! + + An empty ("" string) reference name argument indicates that the + mailbox name is interpreted as by SELECT. The returned mailbox + names MUST match the supplied mailbox name pattern. A non-empty + reference name argument is the name of a mailbox or a level of + mailbox hierarchy, and indicates the context in which the mailbox + name is interpreted. + + An empty ("" string) mailbox name argument is a special request to + return the hierarchy delimiter and the root name of the name given + in the reference. The value returned as the root MAY be the empty + string if the reference is non-rooted or is an empty string. In + all cases, a hierarchy delimiter (or NIL if there is no hierarchy) + is returned. This permits a client to get the hierarchy delimiter + (or find out that the mailbox names are flat) even when no + mailboxes by that name currently exist. + + The reference and mailbox name arguments are interpreted into a + canonical form that represents an unambiguous left-to-right + hierarchy. The returned mailbox names will be in the interpreted + form. + + Note: The interpretation of the reference argument is + implementation-defined. It depends upon whether the + server implementation has a concept of the "current + working directory" and leading "break out characters", + which override the current working directory. + + For example, on a server which exports a UNIX or NT + filesystem, the reference argument contains the current + working directory, and the mailbox name argument would + contain the name as interpreted in the current working + directory. + + If a server implementation has no concept of break out + characters, the canonical form is normally the reference + name appended with the mailbox name. Note that if the + server implements the namespace convention (section + 5.1.2), "#" is a break out character and must be treated + as such. + + If the reference argument is not a level of mailbox + hierarchy (that is, it is a \NoInferiors name), and/or + the reference argument does not end with the hierarchy + delimiter, it is implementation-dependent how this is + interpreted. For example, a reference of "foo/bar" and + mailbox name of "rag/baz" could be interpreted as + "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/baz". + A client SHOULD NOT use such a reference argument except + at the explicit request of the user. A hierarchical + browser MUST NOT make any assumptions about server + interpretation of the reference unless the reference is + a level of mailbox hierarchy AND ends with the hierarchy + delimiter. + + Any part of the reference argument that is included in the + interpreted form SHOULD prefix the interpreted form. It SHOULD + also be in the same form as the reference name argument. This + rule permits the client to determine if the returned mailbox name + is in the context of the reference argument, or if something about + the mailbox argument overrode the reference argument. Without + this rule, the client would have to have knowledge of the server's + naming semantics including what characters are "breakouts" that + override a naming context. + + For example, here are some examples of how references + and mailbox names might be interpreted on a UNIX-based + server: + + Reference Mailbox Name Interpretation + ------------ ------------ -------------- + ~smith/Mail/ foo.* ~smith/Mail/foo.* + archive/ % archive/% + #news. comp.mail.* #news.comp.mail.* + ~smith/Mail/ /usr/doc/foo /usr/doc/foo + archive/ ~fred/Mail/* ~fred/Mail/* + + The first three examples demonstrate interpretations in + the context of the reference argument. Note that + "~smith/Mail" SHOULD NOT be transformed into something + like "/u2/users/smith/Mail", or it would be impossible + for the client to determine that the interpretation was + in the context of the reference. + + The character "*" is a wildcard, and matches zero or more + characters at this position. The character "%" is similar to "*", + but it does not match a hierarchy delimiter. If the "%" wildcard + is the last character of a mailbox name argument, matching levels + of hierarchy are also returned. If these levels of hierarchy are + not also selectable mailboxes, they are returned with the + \Noselect mailbox name attribute (see the description of the LIST + response for more details). + + Server implementations are permitted to "hide" otherwise + accessible mailboxes from the wildcard characters, by preventing + certain characters or names from matching a wildcard in certain + situations. For example, a UNIX-based server might restrict the + interpretation of "*" so that an initial "/" character does not + match. + + The special name INBOX is included in the output from LIST, if + INBOX is supported by this server for this user and if the + uppercase string "INBOX" matches the interpreted reference and + mailbox name arguments with wildcards as described above. The + criteria for omitting INBOX is whether SELECT INBOX will return + failure; it is not relevant whether the user's real INBOX resides + on this or some other server. + + Example: C: A101 LIST "" "" + S: * LIST (\Noselect) "/" "" + S: A101 OK LIST Completed + C: A102 LIST #news.comp.mail.misc "" + S: * LIST (\Noselect) "." #news. + S: A102 OK LIST Completed + C: A103 LIST /usr/staff/jones "" + S: * LIST (\Noselect) "/" / + S: A103 OK LIST Completed + C: A202 LIST ~/Mail/ % + S: * LIST (\Noselect) "/" ~/Mail/foo + S: * LIST () "/" ~/Mail/meetings + S: A202 OK LIST completed + +6.3.9. LSUB Command + + Arguments: reference name + mailbox name with possible wildcards + + Responses: untagged responses: LSUB + + Result: OK - lsub completed + NO - lsub failure: can't list that reference or name + BAD - command unknown or arguments invalid + + The LSUB command returns a subset of names from the set of names + that the user has declared as being "active" or "subscribed". + Zero or more untagged LSUB replies are returned. The arguments to + LSUB are in the same form as those for LIST. + + The returned untagged LSUB response MAY contain different mailbox + flags from a LIST untagged response. If this should happen, the + flags in the untagged LIST are considered more authoritative. + + A special situation occurs when using LSUB with the % wildcard. + Consider what happens if "foo/bar" (with a hierarchy delimiter of + "/") is subscribed but "foo" is not. A "%" wildcard to LSUB must + return foo, not foo/bar, in the LSUB response, and it MUST be + flagged with the \Noselect attribute. + + The server MUST NOT unilaterally remove an existing mailbox name + from the subscription list even if a mailbox by that name no + longer exists. + + Example: C: A002 LSUB "#news." "comp.mail.*" + S: * LSUB () "." #news.comp.mail.mime + S: * LSUB () "." #news.comp.mail.misc + S: A002 OK LSUB completed + C: A003 LSUB "#news." "comp.%" + S: * LSUB (\NoSelect) "." #news.comp.mail + S: A003 OK LSUB completed + +6.3.10. STATUS Command + + Arguments: mailbox name + status data item names + + Responses: untagged responses: STATUS + + Result: OK - status completed + NO - status failure: no status for that name + BAD - command unknown or arguments invalid + + The STATUS command requests the status of the indicated mailbox. + It does not change the currently selected mailbox, nor does it + affect the state of any messages in the queried mailbox (in + particular, STATUS MUST NOT cause messages to lose the \Recent + flag). + + The STATUS command provides an alternative to opening a second + IMAP4rev1 connection and doing an EXAMINE command on a mailbox to + query that mailbox's status without deselecting the current + mailbox in the first IMAP4rev1 connection. + + Unlike the LIST command, the STATUS command is not guaranteed to + be fast in its response. Under certain circumstances, it can be + quite slow. In some implementations, the server is obliged to + open the mailbox read-only internally to obtain certain status + information. Also unlike the LIST command, the STATUS command + does not accept wildcards. + + Note: The STATUS command is intended to access the + status of mailboxes other than the currently selected + mailbox. Because the STATUS command can cause the + mailbox to be opened internally, and because this + information is available by other means on the selected + mailbox, the STATUS command SHOULD NOT be used on the + currently selected mailbox. + + The STATUS command MUST NOT be used as a "check for new + messages in the selected mailbox" operation (refer to + sections 7, 7.3.1, and 7.3.2 for more information about + the proper method for new message checking). + + Because the STATUS command is not guaranteed to be fast + in its results, clients SHOULD NOT expect to be able to + issue many consecutive STATUS commands and obtain + reasonable performance. + + The currently defined status data items that can be requested are: + + MESSAGES + The number of messages in the mailbox. + + RECENT + The number of messages with the \Recent flag set. + + UIDNEXT + The next unique identifier value of the mailbox. Refer to + section 2.3.1.1 for more information. + + UIDVALIDITY + The unique identifier validity value of the mailbox. Refer to + section 2.3.1.1 for more information. + + UNSEEN + The number of messages which do not have the \Seen flag set. + + Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES) + S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292) + S: A042 OK STATUS completed + +6.3.11. APPEND Command + + Arguments: mailbox name + OPTIONAL flag parenthesized list + OPTIONAL date/time string + message literal + + Responses: no specific responses for this command + + Result: OK - append completed + NO - append error: can't append to that mailbox, error + in flags or date/time or message text + BAD - command unknown or arguments invalid + + The APPEND command appends the literal argument as a new message + to the end of the specified destination mailbox. This argument + SHOULD be in the format of an [_R_F_C_-_2_8_2_2] message. 8-bit + characters are permitted in the message. A server implementation + that is unable to preserve 8-bit data properly MUST be able to + reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB] + content transfer encoding. + + Note: There MAY be exceptions, e.g., draft messages, in + which required [_R_F_C_-_2_8_2_2] header lines are omitted in + the message literal argument to APPEND. The full + implications of doing so MUST be understood and + carefully weighed. + + If a flag parenthesized list is specified, the flags SHOULD be set + in the resulting message; otherwise, the flag list of the + resulting message is set to empty by default. In either case, the + Recent flag is also set. + + If a date-time is specified, the internal date SHOULD be set in + the resulting message; otherwise, the internal date of the + resulting message is set to the current date and time by default. + + If the append is unsuccessful for any reason, the mailbox MUST be + restored to its state before the APPEND attempt; no partial + appending is permitted. + + If the destination mailbox does not exist, a server MUST return an + error, and MUST NOT automatically create the mailbox. Unless it + is certain that the destination mailbox can not be created, the + server MUST send the response code "[TRYCREATE]" as the prefix of + the text of the tagged NO response. This gives a hint to the + client that it can attempt a CREATE command and retry the APPEND + if the CREATE is successful. + + If the mailbox is currently selected, the normal new message + actions SHOULD occur. Specifically, the server SHOULD notify the + client immediately via an untagged EXISTS response. If the server + does not do so, the client MAY issue a NOOP command (or failing + that, a CHECK command) after one or more APPEND commands. + + Example: C: A003 APPEND saved-messages (\Seen) {310} + S: + Ready for literal data + C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST) + C: From: Fred Foobar <_f_o_o_b_a_r_@_B_l_u_r_d_y_b_l_o_o_p_._C_O_M> + C: Subject: afternoon meeting + C: To: _m_o_o_c_h_@_o_w_a_t_a_g_u_._s_i_a_m_._e_d_u + C: Message-Id: <B27397-0100000@Blurdybloop.COM> + C: MIME-Version: 1.0 + C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII + C: + C: Hello Joe, do you think we can meet at 3:30 tomorrow? + C: + S: A003 OK APPEND completed + + Note: The APPEND command is not used for message delivery, + because it does not provide a mechanism to transfer [SMTP] + envelope information. + +6.4. Client Commands - Selected State + + In the selected state, commands that manipulate messages in a mailbox + are permitted. + + In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT), + and the authenticated state commands (SELECT, EXAMINE, CREATE, + DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and + APPEND), the following commands are valid in the selected state: + CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID. + +6.4.1. CHECK Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - check completed + BAD - command unknown or arguments invalid + + The CHECK command requests a checkpoint of the currently selected + mailbox. A checkpoint refers to any implementation-dependent + housekeeping associated with the mailbox (e.g., resolving the + server's in-memory state of the mailbox with the state on its + + disk) that is not normally executed as part of each command. A + checkpoint MAY take a non-instantaneous amount of real time to + complete. If a server implementation has no such housekeeping + considerations, CHECK is equivalent to NOOP. + + There is no guarantee that an EXISTS untagged response will happen + as a result of CHECK. NOOP, not CHECK, SHOULD be used for new + message polling. + + Example: C: FXXZ CHECK + S: FXXZ OK CHECK Completed + +6.4.2. CLOSE Command + + Arguments: none + + Responses: no specific responses for this command + + Result: OK - close completed, now in authenticated state + BAD - command unknown or arguments invalid + + The CLOSE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox, and returns + to the authenticated state from the selected state. No untagged + EXPUNGE responses are sent. + + No messages are removed, and no error is given, if the mailbox is + selected by an EXAMINE command or is otherwise selected read-only. + + Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT + command MAY be issued without previously issuing a CLOSE command. + The SELECT, EXAMINE, and LOGOUT commands implicitly close the + currently selected mailbox without doing an expunge. However, + when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT + sequence is considerably faster than an EXPUNGE-LOGOUT or + EXPUNGE-SELECT because no untagged EXPUNGE responses (which the + client would probably ignore) are sent. + + Example: C: A341 CLOSE + S: A341 OK CLOSE completed + +6.4.3. EXPUNGE Command + + Arguments: none + + Responses: untagged responses: EXPUNGE + + Result: OK - expunge completed + NO - expunge failure: can't expunge (e.g., permission + denied) + BAD - command unknown or arguments invalid + + The EXPUNGE command permanently removes all messages that have the + \Deleted flag set from the currently selected mailbox. Before + returning an OK to the client, an untagged EXPUNGE response is + sent for each message that is removed. + + Example: C: A202 EXPUNGE + S: * 3 EXPUNGE + S: * 3 EXPUNGE + S: * 5 EXPUNGE + S: * 8 EXPUNGE + S: A202 OK EXPUNGE completed + + Note: In this example, messages 3, 4, 7, and 11 had the + \Deleted flag set. See the description of the EXPUNGE + response for further explanation. + +6.4.4. SEARCH Command + + Arguments: OPTIONAL [CHARSET] specification + searching criteria (one or more) + + Responses: REQUIRED untagged response: SEARCH + + Result: OK - search completed + NO - search error: can't search that [CHARSET] or + criteria + BAD - command unknown or arguments invalid + + The SEARCH command searches the mailbox for messages that match + the given searching criteria. Searching criteria consist of one + or more search keys. The untagged SEARCH response from the server + contains a listing of message sequence numbers corresponding to + those messages that match the searching criteria. + + When multiple keys are specified, the result is the intersection + (AND function) of all the messages that match those keys. For + example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers + to all deleted messages from Smith that were placed in the mailbox + since February 1, 1994. A search key can also be a parenthesized + list of one or more search keys (e.g., for use with the OR and NOT + keys). + + Server implementations MAY exclude [MIME-IMB] body parts with + terminal content media types other than TEXT and MESSAGE from + consideration in SEARCH matching. + + The OPTIONAL [CHARSET] specification consists of the word + "CHARSET" followed by a registered [CHARSET]. It indicates the + [CHARSET] of the strings that appear in the search criteria. + [MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in + [_R_F_C_-_2_8_2_2]/[MIME-IMB] headers, MUST be decoded before comparing + text in a [CHARSET] other than US-ASCII. US-ASCII MUST be + supported; other [CHARSET]s MAY be supported. + + If the server does not support the specified [CHARSET], it MUST + return a tagged NO response (not a BAD). This response SHOULD + contain the BADCHARSET response code, which MAY list the + [CHARSET]s supported by the server. + + In all search keys that use strings, a message matches the key if + the string is a substring of the field. The matching is + case-insensitive. + + The defined search keys are as follows. Refer to the Formal + Syntax section for the precise syntactic definitions of the + arguments. + + <sequence set> + Messages with message sequence numbers corresponding to the + specified message sequence number set. + + ALL + All messages in the mailbox; the default initial key for + ANDing. + + ANSWERED + Messages with the \Answered flag set. + + BCC <string> + Messages that contain the specified string in the envelope + structure's BCC field. + + BEFORE <date> + Messages whose internal date (disregarding time and timezone) + is earlier than the specified date. + + BODY <string> + Messages that contain the specified string in the body of the + message. + + CC <string> + Messages that contain the specified string in the envelope + structure's CC field. + + DELETED + Messages with the \Deleted flag set. + + DRAFT + Messages with the \Draft flag set. + + FLAGGED + Messages with the \Flagged flag set. + + FROM <string> + Messages that contain the specified string in the envelope + structure's FROM field. + + HEADER <field-name> <string> + Messages that have a header with the specified field-name (as + defined in [_R_F_C_-_2_8_2_2]) and that contains the specified string + in the text of the header (what comes after the colon). If the + string to search is zero-length, this matches all messages that + have a header line with the specified field-name regardless of + the contents. + + KEYWORD <flag> + Messages with the specified keyword flag set. + + LARGER <n> + Messages with an [_R_F_C_-_2_8_2_2] size larger than the specified + number of octets. + + NEW + Messages that have the \Recent flag set but not the \Seen flag. + This is functionally equivalent to "(RECENT UNSEEN)". + + NOT <search-key> + Messages that do not match the specified search key. + + OLD + Messages that do not have the \Recent flag set. This is + functionally equivalent to "NOT RECENT" (as opposed to "NOT + NEW"). + + ON <date> + Messages whose internal date (disregarding time and timezone) + is within the specified date. + + OR <search-key1> <search-key2> + Messages that match either search key. + + RECENT + Messages that have the \Recent flag set. + + SEEN + Messages that have the \Seen flag set. + + SENTBEFORE <date> + Messages whose [_R_F_C_-_2_8_2_2] Date: header (disregarding time and + timezone) is earlier than the specified date. + + SENTON <date> + Messages whose [_R_F_C_-_2_8_2_2] Date: header (disregarding time and + timezone) is within the specified date. + + SENTSINCE <date> + Messages whose [_R_F_C_-_2_8_2_2] Date: header (disregarding time and + timezone) is within or later than the specified date. + + SINCE <date> + Messages whose internal date (disregarding time and timezone) + is within or later than the specified date. + + SMALLER <n> + Messages with an [_R_F_C_-_2_8_2_2] size smaller than the specified + number of octets. + + SUBJECT <string> + Messages that contain the specified string in the envelope + structure's SUBJECT field. + + TEXT <string> + Messages that contain the specified string in the header or + body of the message. + + TO <string> + Messages that contain the specified string in the envelope + structure's TO field. + + UID <sequence set> + Messages with unique identifiers corresponding to the specified + unique identifier set. Sequence set ranges are permitted. + + UNANSWERED + Messages that do not have the \Answered flag set. + + UNDELETED + Messages that do not have the \Deleted flag set. + + UNDRAFT + Messages that do not have the \Draft flag set. + + UNFLAGGED + Messages that do not have the \Flagged flag set. + + UNKEYWORD <flag> + Messages that do not have the specified keyword flag set. + + UNSEEN + Messages that do not have the \Seen flag set. + + Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith" + S: * SEARCH 2 84 882 + S: A282 OK SEARCH completed + C: A283 SEARCH TEXT "string not in mailbox" + S: * SEARCH + S: A283 OK SEARCH completed + C: A284 SEARCH CHARSET UTF-8 TEXT {6} + C: XXXXXX + S: * SEARCH 43 + S: A284 OK SEARCH completed + + Note: Since this document is restricted to 7-bit ASCII + text, it is not possible to show actual UTF-8 data. The + "XXXXXX" is a placeholder for what would be 6 octets of + 8-bit data in an actual transaction. + +6.4.5. FETCH Command + + Arguments: sequence set + message data item names or macro + + Responses: untagged responses: FETCH + + Result: OK - fetch completed + NO - fetch error: can't fetch that data + BAD - command unknown or arguments invalid + + The FETCH command retrieves data associated with a message in the + mailbox. The data items to be fetched can be either a single atom + or a parenthesized list. + + Most data items, identified in the formal syntax under the + msg-att-static rule, are static and MUST NOT change for any + particular message. Other data items, identified in the formal + syntax under the msg-att-dynamic rule, MAY change, either as a + result of a STORE command or due to external events. + + For example, if a client receives an ENVELOPE for a + message when it already knows the envelope, it can + safely ignore the newly transmitted envelope. + + There are three macros which specify commonly-used sets of data + items, and can be used instead of data items. A macro must be + used by itself, and not in conjunction with other macros or data + items. + + ALL + Macro equivalent to: (FLAGS INTERNALDATE _R_F_C_8_2_2.SIZE ENVELOPE) + + FAST + Macro equivalent to: (FLAGS INTERNALDATE _R_F_C_8_2_2.SIZE) + + FULL + Macro equivalent to: (FLAGS INTERNALDATE _R_F_C_8_2_2.SIZE ENVELOPE + BODY) + + The currently defined data items that can be fetched are: + + BODY + Non-extensible form of BODYSTRUCTURE. + + BODY[<section>]<<partial>> + The text of a particular body section. The section + specification is a set of zero or more part specifiers + delimited by periods. A part specifier is either a part number + or one of the following: HEADER, HEADER.FIELDS, + HEADER.FIELDS.NOT, MIME, and TEXT. An empty section + specification refers to the entire message, including the + header. + + Every message has at least one part number. Non-[MIME-IMB] + messages, and non-multipart [MIME-IMB] messages with no + encapsulated message, only have a part 1. + + Multipart messages are assigned consecutive part numbers, as + they occur in the message. If a particular part is of type + message or multipart, its parts MUST be indicated by a period + followed by the part number within that nested multipart part. + + A part of type MESSAGE/RFC822 also has nested part numbers, + referring to parts of the MESSAGE part's body. + + The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part + specifiers can be the sole part specifier or can be prefixed by + one or more numeric part specifiers, provided that the numeric + part specifier refers to a part of type MESSAGE/RFC822. The + MIME part specifier MUST be prefixed by one or more numeric + part specifiers. + + The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part + specifiers refer to the [_R_F_C_-_2_8_2_2] header of the message or of + an encapsulated [MIME-IMT] MESSAGE/RFC822 message. + HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of + field-name (as defined in [_R_F_C_-_2_8_2_2]) names, and return a + + subset of the header. The subset returned by HEADER.FIELDS + contains only those header fields with a field-name that + matches one of the names in the list; similarly, the subset + returned by HEADER.FIELDS.NOT contains only the header fields + with a non-matching field-name. The field-matching is + case-insensitive but otherwise exact. Subsetting does not + exclude the [_R_F_C_-_2_8_2_2] delimiting blank line between the header + and the body; the blank line is included in all header fetches, + except in the case of a message which has no body and no blank + line. + + The MIME part specifier refers to the [MIME-IMB] header for + this part. + + The TEXT part specifier refers to the text body of the message, + omitting the [_R_F_C_-_2_8_2_2] header. + + Here is an example of a complex message with some of its + part specifiers: + + HEADER ([_R_F_C_-_2_8_2_2] header of the message) + TEXT ([_R_F_C_-_2_8_2_2] text body of the message) MULTIPART/MIXED + 1 TEXT/PLAIN + 2 APPLICATION/OCTET-STREAM + 3 MESSAGE/RFC822 + 3.HEADER ([_R_F_C_-_2_8_2_2] header of the message) + 3.TEXT ([_R_F_C_-_2_8_2_2] text body of the message) MULTIPART/MIXED + 3.1 TEXT/PLAIN + 3.2 APPLICATION/OCTET-STREAM + 4 MULTIPART/MIXED + 4.1 IMAGE/GIF + 4.1.MIME ([MIME-IMB] header for the IMAGE/GIF) + 4.2 MESSAGE/RFC822 + 4.2.HEADER ([_R_F_C_-_2_8_2_2] header of the message) + 4.2.TEXT ([_R_F_C_-_2_8_2_2] text body of the message) MULTIPART/MIXED + 4.2.1 TEXT/PLAIN + 4.2.2 MULTIPART/ALTERNATIVE + 4.2.2.1 TEXT/PLAIN + 4.2.2.2 TEXT/RICHTEXT + + It is possible to fetch a substring of the designated text. + This is done by appending an open angle bracket ("<"), the + octet position of the first desired octet, a period, the + maximum number of octets desired, and a close angle bracket + (">") to the part specifier. If the starting octet is beyond + the end of the text, an empty string is returned. + + Any partial fetch that attempts to read beyond the end of the + text is truncated as appropriate. A partial fetch that starts + at octet 0 is returned as a partial fetch, even if this + truncation happened. + + Note: This means that BODY[]<0.2048> of a 1500-octet message + will return BODY[]<0> with a literal of size 1500, not + BODY[]. + + Note: A substring fetch of a HEADER.FIELDS or + HEADER.FIELDS.NOT part specifier is calculated after + subsetting the header. + + The \Seen flag is implicitly set; if this causes the flags to + change, they SHOULD be included as part of the FETCH responses. + + BODY.PEEK[<section>]<<partial>> + An alternate form of BODY[<section>] that does not implicitly + set the \Seen flag. + + BODYSTRUCTURE + The [MIME-IMB] body structure of the message. This is computed + by the server by parsing the [MIME-IMB] header fields in the + [_R_F_C_-_2_8_2_2] header and [MIME-IMB] headers. + + ENVELOPE + The envelope structure of the message. This is computed by the + server by parsing the [_R_F_C_-_2_8_2_2] header into the component + parts, defaulting various fields as necessary. + + FLAGS + The flags that are set for this message. + + INTERNALDATE + The internal date of the message. + + _R_F_C_8_2_2 + Functionally equivalent to BODY[], differing in the syntax of + the resulting untagged FETCH data (_R_F_C_8_2_2 is returned). + + _R_F_C_8_2_2.HEADER + Functionally equivalent to BODY.PEEK[HEADER], differing in the + syntax of the resulting untagged FETCH data (_R_F_C_8_2_2.HEADER is + returned). + + _R_F_C_8_2_2.SIZE + The [_R_F_C_-_2_8_2_2] size of the message. + + _R_F_C_8_2_2.TEXT + Functionally equivalent to BODY[TEXT], differing in the syntax + of the resulting untagged FETCH data (_R_F_C_8_2_2.TEXT is returned). + + UID + The unique identifier for the message. + + Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)]) + S: * 2 FETCH .... + S: * 3 FETCH .... + S: * 4 FETCH .... + S: A654 OK FETCH completed + +6.4.6. STORE Command + + Arguments: sequence set + message data item name + value for message data item + + Responses: untagged responses: FETCH + + Result: OK - store completed + NO - store error: can't store that data + BAD - command unknown or arguments invalid + + The STORE command alters data associated with a message in the + mailbox. Normally, STORE will return the updated value of the + data with an untagged FETCH response. A suffix of ".SILENT" in + the data item name prevents the untagged FETCH, and the server + SHOULD assume that the client has determined the updated value + itself or does not care about the updated value. + + Note: Regardless of whether or not the ".SILENT" suffix + was used, the server SHOULD send an untagged FETCH + response if a change to a message's flags from an + external source is observed. The intent is that the + status of the flags is determinate without a race + condition. + + The currently defined data items that can be stored are: + + FLAGS <flag list> + Replace the flags for the message (other than \Recent) with the + argument. The new value of the flags is returned as if a FETCH + of those flags was done. + + FLAGS.SILENT <flag list> + Equivalent to FLAGS, but without returning a new value. + + +FLAGS <flag list> + Add the argument to the flags for the message. The new value + of the flags is returned as if a FETCH of those flags was done. + + +FLAGS.SILENT <flag list> + Equivalent to +FLAGS, but without returning a new value. + + -FLAGS <flag list> + Remove the argument from the flags for the message. The new + value of the flags is returned as if a FETCH of those flags was + done. + + -FLAGS.SILENT <flag list> + Equivalent to -FLAGS, but without returning a new value. + + Example: C: A003 STORE 2:4 +FLAGS (\Deleted) + S: * 2 FETCH (FLAGS (\Deleted \Seen)) + S: * 3 FETCH (FLAGS (\Deleted)) + S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen)) + S: A003 OK STORE completed + +6.4.7. COPY Command + + Arguments: sequence set + mailbox name + + Responses: no specific responses for this command + + Result: OK - copy completed + NO - copy error: can't copy those messages or to that + name + BAD - command unknown or arguments invalid + + The COPY command copies the specified message(s) to the end of the + specified destination mailbox. The flags and internal date of the + message(s) SHOULD be preserved, and the Recent flag SHOULD be set, + in the copy. + + If the destination mailbox does not exist, a server SHOULD return + an error. It SHOULD NOT automatically create the mailbox. Unless + it is certain that the destination mailbox can not be created, the + server MUST send the response code "[TRYCREATE]" as the prefix of + the text of the tagged NO response. This gives a hint to the + client that it can attempt a CREATE command and retry the COPY if + the CREATE is successful. + + If the COPY command is unsuccessful for any reason, server + implementations MUST restore the destination mailbox to its state + before the COPY attempt. + + Example: C: A003 COPY 2:4 MEETING + S: A003 OK COPY completed + +6.4.8. UID Command + + Arguments: command name + command arguments + + Responses: untagged responses: FETCH, SEARCH + + Result: OK - UID command completed + NO - UID command error + BAD - command unknown or arguments invalid + + The UID command has two forms. In the first form, it takes as its + arguments a COPY, FETCH, or STORE command with arguments + appropriate for the associated command. However, the numbers in + the sequence set argument are unique identifiers instead of + message sequence numbers. Sequence set ranges are permitted, but + there is no guarantee that unique identifiers will be contiguous. + + A non-existent unique identifier is ignored without any error + message generated. Thus, it is possible for a UID FETCH command + to return an OK without any data or a UID COPY or UID STORE to + return an OK without performing any operations. + + In the second form, the UID command takes a SEARCH command with + SEARCH command arguments. The interpretation of the arguments is + the same as with SEARCH; however, the numbers returned in a SEARCH + response for a UID SEARCH command are unique identifiers instead + + of message sequence numbers. For example, the command UID SEARCH + 1:100 UID 443:557 returns the unique identifiers corresponding to + the intersection of two sequence sets, the message sequence number + range 1:100 and the UID range 443:557. + + Note: in the above example, the UID range 443:557 + appears. The same comment about a non-existent unique + identifier being ignored without any error message also + applies here. Hence, even if neither UID 443 or 557 + exist, this range is valid and would include an existing + UID 495. + + Also note that a UID range of 559:* always includes the + UID of the last message in the mailbox, even if 559 is + higher than any assigned UID value. This is because the + contents of a range are independent of the order of the + range endpoints. Thus, any UID range with * as one of + the endpoints indicates at least one message (the + message with the highest numbered UID), unless the + mailbox is empty. + + The number after the "*" in an untagged FETCH response is always a + message sequence number, not a unique identifier, even for a UID + command response. However, server implementations MUST implicitly + include the UID message data item as part of any FETCH response + caused by a UID command, regardless of whether a UID was specified + as a message data item to the FETCH. + + Note: The rule about including the UID message data item as part + of a FETCH response primarily applies to the UID FETCH and UID + STORE commands, including a UID FETCH command that does not + include UID as a message data item. Although it is unlikely that + the other UID commands will cause an untagged FETCH, this rule + applies to these commands as well. + + Example: C: A999 UID FETCH 4827313:4828442 FLAGS + S: * 23 FETCH (FLAGS (\Seen) UID 4827313) + S: * 24 FETCH (FLAGS (\Seen) UID 4827943) + S: * 25 FETCH (FLAGS (\Seen) UID 4828442) + S: A999 OK UID FETCH completed + +6.5. Client Commands - Experimental/Expansion + +6.5.1. X<atom> Command + + Arguments: implementation defined + + Responses: implementation defined + + Result: OK - command completed + NO - failure + BAD - command unknown or arguments invalid + + Any command prefixed with an X is an experimental command. + Commands which are not part of this specification, a standard or + standards-track revision of this specification, or an + IESG-approved experimental protocol, MUST use the X prefix. + + Any added untagged responses issued by an experimental command + MUST also be prefixed with an X. Server implementations MUST NOT + send any such untagged responses, unless the client requested it + by issuing the associated experimental command. + + Example: C: a441 CAPABILITY + S: * CAPABILITY IMAP4rev1 XPIG-LATIN + S: a441 OK CAPABILITY completed + C: A442 XPIG-LATIN + S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay + S: A442 OK XPIG-LATIN ompleted-cay + +7. Server Responses + + Server responses are in three forms: status responses, server data, + and command continuation request. The information contained in a + server response, identified by "Contents:" in the response + descriptions below, is described by function, not by syntax. The + precise syntax of server responses is described in the Formal Syntax + section. + + The client MUST be prepared to accept any response at all times. + + Status responses can be tagged or untagged. Tagged status responses + indicate the completion result (OK, NO, or BAD status) of a client + command, and have a tag matching the command. + + Some status responses, and all server data, are untagged. An + untagged response is indicated by the token "*" instead of a tag. + Untagged status responses indicate server greeting, or server status + + that does not indicate the completion of a command (for example, an + impending system shutdown alert). For historical reasons, untagged + server data responses are also called "unsolicited data", although + strictly speaking, only unilateral server data is truly + "unsolicited". + + Certain server data MUST be recorded by the client when it is + received; this is noted in the description of that data. Such data + conveys critical information which affects the interpretation of all + subsequent commands and responses (e.g., updates reflecting the + creation or destruction of messages). + + Other server data SHOULD be recorded for later reference; if the + client does not need to record the data, or if recording the data has + no obvious purpose (e.g., a SEARCH response when no SEARCH command is + in progress), the data SHOULD be ignored. + + An example of unilateral untagged server data occurs when the IMAP + connection is in the selected state. In the selected state, the + server checks the mailbox for new messages as part of command + execution. Normally, this is part of the execution of every command; + hence, a NOOP command suffices to check for new messages. If new + messages are found, the server sends untagged EXISTS and RECENT + responses reflecting the new size of the mailbox. Server + implementations that offer multiple simultaneous access to the same + mailbox SHOULD also send appropriate unilateral untagged FETCH and + EXPUNGE responses if another agent changes the state of any message + flags or expunges any messages. + + Command continuation request responses use the token "+" instead of a + tag. These responses are sent by the server to indicate acceptance + of an incomplete client command and readiness for the remainder of + the command. + +7.1. Server Responses - Status Responses + + Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD + can be tagged or untagged. PREAUTH and BYE are always untagged. + + Status responses MAY include an OPTIONAL "response code". A response + code consists of data inside square brackets in the form of an atom, + possibly followed by a space and arguments. The response code + contains additional information or status codes for client software + beyond the OK/NO/BAD condition, and are defined when there is a + specific action that a client can take based upon the additional + information. + + The currently defined response codes are: + + ALERT + + The human-readable text contains a special alert that MUST be + presented to the user in a fashion that calls the user's + attention to the message. + + BADCHARSET + + Optionally followed by a parenthesized list of charsets. A + SEARCH failed because the given charset is not supported by + this implementation. If the optional list of charsets is + given, this lists the charsets that are supported by this + implementation. + + CAPABILITY + + Followed by a list of capabilities. This can appear in the + initial OK or PREAUTH response to transmit an initial + capabilities list. This makes it unnecessary for a client to + send a separate CAPABILITY command if it recognizes this + response. + + PARSE + + The human-readable text represents an error in parsing the + [_R_F_C_-_2_8_2_2] header or [MIME-IMB] headers of a message in the + mailbox. + + PERMANENTFLAGS + + Followed by a parenthesized list of flags, indicates which of + the known flags the client can change permanently. Any flags + that are in the FLAGS untagged response, but not the + PERMANENTFLAGS list, can not be set permanently. If the client + attempts to STORE a flag that is not in the PERMANENTFLAGS + list, the server will either ignore the change or store the + state change for the remainder of the current session only. + The PERMANENTFLAGS list can also include the special flag \*, + which indicates that it is possible to create new keywords by + attempting to store those flags in the mailbox. + + READ-ONLY + + The mailbox is selected read-only, or its access while selected + has changed from read-write to read-only. + + READ-WRITE + + The mailbox is selected read-write, or its access while + selected has changed from read-only to read-write. + + TRYCREATE + + An APPEND or COPY attempt is failing because the target mailbox + does not exist (as opposed to some other reason). This is a + hint to the client that the operation can succeed if the + mailbox is first created by the CREATE command. + + UIDNEXT + + Followed by a decimal number, indicates the next unique + identifier value. Refer to section 2.3.1.1 for more + information. + + UIDVALIDITY + + Followed by a decimal number, indicates the unique identifier + validity value. Refer to section 2.3.1.1 for more information. + + UNSEEN + + Followed by a decimal number, indicates the number of the first + message without the \Seen flag set. + + Additional response codes defined by particular client or server + implementations SHOULD be prefixed with an "X" until they are + added to a revision of this protocol. Client implementations + SHOULD ignore response codes that they do not recognize. + +7.1.1. OK Response + + Contents: OPTIONAL response code + human-readable text + + The OK response indicates an information message from the server. + When tagged, it indicates successful completion of the associated + command. The human-readable text MAY be presented to the user as + an information message. The untagged form indicates an + + information-only message; the nature of the information MAY be + indicated by a response code. + + The untagged form is also used as one of three possible greetings + at connection startup. It indicates that the connection is not + yet authenticated and that a LOGIN command is needed. + + Example: S: * OK IMAP4rev1 server ready + C: A001 LOGIN fred blurdybloop + S: * OK [ALERT] System shutdown in 10 minutes + S: A001 OK LOGIN Completed + +7.1.2. NO Response + + Contents: OPTIONAL response code + human-readable text + + The NO response indicates an operational error message from the + server. When tagged, it indicates unsuccessful completion of the + associated command. The untagged form indicates a warning; the + command can still complete successfully. The human-readable text + describes the condition. + + Example: C: A222 COPY 1:2 owatagusiam + S: * NO Disk is 98% full, please delete unnecessary data + S: A222 OK COPY completed + C: A223 COPY 3:200 blurdybloop + S: * NO Disk is 98% full, please delete unnecessary data + S: * NO Disk is 99% full, please delete unnecessary data + S: A223 NO COPY failed: disk is full + +7.1.3. BAD Response + + Contents: OPTIONAL response code + human-readable text + + The BAD response indicates an error message from the server. When + tagged, it reports a protocol-level error in the client's command; + the tag indicates the command that caused the error. The untagged + form indicates a protocol-level error for which the associated + command can not be determined; it can also indicate an internal + server failure. The human-readable text describes the condition. + + Example: C: ...very long command line... + S: * BAD Command line too long + C: ...empty line... + S: * BAD Empty command line + C: A443 EXPUNGE + S: * BAD Disk crash, attempting salvage to a new disk! + S: * OK Salvage successful, no data lost + S: A443 OK Expunge completed + +7.1.4. PREAUTH Response + + Contents: OPTIONAL response code + human-readable text + + The PREAUTH response is always untagged, and is one of three + possible greetings at connection startup. It indicates that the + connection has already been authenticated by external means; thus + no LOGIN command is needed. + + Example: S: * PREAUTH IMAP4rev1 server logged in as Smith + +7.1.5. BYE Response + + Contents: OPTIONAL response code + human-readable text + + The BYE response is always untagged, and indicates that the server + is about to close the connection. The human-readable text MAY be + displayed to the user in a status report by the client. The BYE + response is sent under one of four conditions: + + 1) as part of a normal logout sequence. The server will close + the connection after sending the tagged OK response to the + LOGOUT command. + + 2) as a panic shutdown announcement. The server closes the + connection immediately. + + 3) as an announcement of an inactivity autologout. The server + closes the connection immediately. + + 4) as one of three possible greetings at connection startup, + indicating that the server is not willing to accept a + connection from this client. The server closes the + connection immediately. + + The difference between a BYE that occurs as part of a normal + LOGOUT sequence (the first case) and a BYE that occurs because of + a failure (the other three cases) is that the connection closes + immediately in the failure case. In all cases the client SHOULD + continue to read response data from the server until the + connection is closed; this will ensure that any pending untagged + or completion responses are read and processed. + + Example: S: * BYE Autologout; idle for too long + +7.2. Server Responses - Server and Mailbox Status + + These responses are always untagged. This is how server and mailbox + status data are transmitted from the server to the client. Many of + these responses typically result from a command with the same name. + +7.2.1. CAPABILITY Response + + Contents: capability listing + + The CAPABILITY response occurs as a result of a CAPABILITY + command. The capability listing contains a space-separated + listing of capability names that the server supports. The + capability listing MUST include the atom "IMAP4rev1". + + In addition, client and server implementations MUST implement the + STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS]) + capabilities. See the Security Considerations section for + important information. + + A capability name which begins with "AUTH=" indicates that the + server supports that particular authentication mechanism. + + The LOGINDISABLED capability indicates that the LOGIN command is + disabled, and that the server will respond with a tagged NO + response to any attempt to use the LOGIN command even if the user + name and password are valid. An IMAP client MUST NOT issue the + LOGIN command if the server advertises the LOGINDISABLED + capability. + + Other capability names indicate that the server supports an + extension, revision, or amendment to the IMAP4rev1 protocol. + Server responses MUST conform to this document until the client + issues a command that uses the associated capability. + + Capability names MUST either begin with "X" or be standard or + standards-track IMAP4rev1 extensions, revisions, or amendments + registered with IANA. A server MUST NOT offer unregistered or + + non-standard capability names, unless such names are prefixed with + an "X". + + Client implementations SHOULD NOT require any capability name + other than "IMAP4rev1", and MUST ignore any unknown capability + names. + + A server MAY send capabilities automatically, by using the + CAPABILITY response code in the initial PREAUTH or OK responses, + and by sending an updated CAPABILITY response code in the tagged + OK response as part of a successful authentication. It is + unnecessary for a client to send a separate CAPABILITY command if + it recognizes these automatic capabilities. + + Example: S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI XPIG-LATIN + +7.2.2. LIST Response + + Contents: name attributes + hierarchy delimiter + name + + The LIST response occurs as a result of a LIST command. It + returns a single name that matches the LIST specification. There + can be multiple LIST responses for a single LIST command. + + Four name attributes are defined: + + \Noinferiors + It is not possible for any child levels of hierarchy to exist + under this name; no child levels exist now and none can be + created in the future. + + \Noselect + It is not possible to use this name as a selectable mailbox. + + \Marked + The mailbox has been marked "interesting" by the server; the + mailbox probably contains messages that have been added since + the last time the mailbox was selected. + + \Unmarked + The mailbox does not contain any additional messages since the + last time the mailbox was selected. + + If it is not feasible for the server to determine whether or not + the mailbox is "interesting", or if the name is a \Noselect name, + the server SHOULD NOT send either \Marked or \Unmarked. + + The hierarchy delimiter is a character used to delimit levels of + hierarchy in a mailbox name. A client can use it to create child + mailboxes, and to search higher or lower levels of naming + hierarchy. All children of a top-level hierarchy node MUST use + the same separator character. A NIL hierarchy delimiter means + that no hierarchy exists; the name is a "flat" name. + + The name represents an unambiguous left-to-right hierarchy, and + MUST be valid for use as a reference in LIST and LSUB commands. + Unless \Noselect is indicated, the name MUST also be valid as an + argument for commands, such as SELECT, that accept mailbox names. + + Example: S: * LIST (\Noselect) "/" ~/Mail/foo + +7.2.3. LSUB Response + + Contents: name attributes + hierarchy delimiter + name + + The LSUB response occurs as a result of an LSUB command. It + returns a single name that matches the LSUB specification. There + can be multiple LSUB responses for a single LSUB command. The + data is identical in format to the LIST response. + + Example: S: * LSUB () "." #news.comp.mail.misc + +7.2.4 STATUS Response + + Contents: name + status parenthesized list + + The STATUS response occurs as a result of an STATUS command. It + returns the mailbox name that matches the STATUS specification and + the requested mailbox status information. + + Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292) + +7.2.5. SEARCH Response + + Contents: zero or more numbers + + The SEARCH response occurs as a result of a SEARCH or UID SEARCH + command. The number(s) refer to those messages that match the + search criteria. For SEARCH, these are message sequence numbers; + for UID SEARCH, these are unique identifiers. Each number is + delimited by a space. + + Example: S: * SEARCH 2 3 6 + +7.2.6. FLAGS Response + + Contents: flag parenthesized list + + The FLAGS response occurs as a result of a SELECT or EXAMINE + command. The flag parenthesized list identifies the flags (at a + minimum, the system-defined flags) that are applicable for this + mailbox. Flags other than the system flags can also exist, + depending on server implementation. + + The update from the FLAGS response MUST be recorded by the client. + + Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) + +7.3. Server Responses - Mailbox Size + + These responses are always untagged. This is how changes in the size + of the mailbox are transmitted from the server to the client. + Immediately following the "*" token is a number that represents a + message count. + +7.3.1. EXISTS Response + + Contents: none + + The EXISTS response reports the number of messages in the mailbox. + This response occurs as a result of a SELECT or EXAMINE command, + and if the size of the mailbox changes (e.g., new messages). + + The update from the EXISTS response MUST be recorded by the + client. + + Example: S: * 23 EXISTS + +7.3.2. RECENT Response + + Contents: none + + The RECENT response reports the number of messages with the + \Recent flag set. This response occurs as a result of a SELECT or + EXAMINE command, and if the size of the mailbox changes (e.g., new + messages). + + Note: It is not guaranteed that the message sequence + numbers of recent messages will be a contiguous range of + the highest n messages in the mailbox (where n is the + value reported by the RECENT response). Examples of + situations in which this is not the case are: multiple + clients having the same mailbox open (the first session + to be notified will see it as recent, others will + probably see it as non-recent), and when the mailbox is + re-ordered by a non-IMAP agent. + + The only reliable way to identify recent messages is to + look at message flags to see which have the \Recent flag + set, or to do a SEARCH RECENT. + + The update from the RECENT response MUST be recorded by the + client. + + Example: S: * 5 RECENT + +7.4. Server Responses - Message Status + + These responses are always untagged. This is how message data are + transmitted from the server to the client, often as a result of a + command with the same name. Immediately following the "*" token is a + number that represents a message sequence number. + +7.4.1. EXPUNGE Response + + Contents: none + + The EXPUNGE response reports that the specified message sequence + number has been permanently removed from the mailbox. The message + sequence number for each successive message in the mailbox is + immediately decremented by 1, and this decrement is reflected in + message sequence numbers in subsequent responses (including other + untagged EXPUNGE responses). + + The EXPUNGE response also decrements the number of messages in the + mailbox; it is not necessary to send an EXISTS response with the + new value. + + As a result of the immediate decrement rule, message sequence + numbers that appear in a set of successive EXPUNGE responses + depend upon whether the messages are removed starting from lower + numbers to higher numbers, or from higher numbers to lower + numbers. For example, if the last 5 messages in a 9-message + mailbox are expunged, a "lower to higher" server will send five + untagged EXPUNGE responses for message sequence number 5, whereas + a "higher to lower server" will send successive untagged EXPUNGE + responses for message sequence numbers 9, 8, 7, 6, and 5. + + An EXPUNGE response MUST NOT be sent when no command is in + progress, nor while responding to a FETCH, STORE, or SEARCH + command. This rule is necessary to prevent a loss of + synchronization of message sequence numbers between client and + server. A command is not "in progress" until the complete command + has been received; in particular, a command is not "in progress" + during the negotiation of command continuation. + + Note: UID FETCH, UID STORE, and UID SEARCH are different + commands from FETCH, STORE, and SEARCH. An EXPUNGE + response MAY be sent during a UID command. + + The update from the EXPUNGE response MUST be recorded by the + client. + + Example: S: * 44 EXPUNGE + +7.4.2. FETCH Response + + Contents: message data + + The FETCH response returns data about a message to the client. + The data are pairs of data item names and their values in + parentheses. This response occurs as the result of a FETCH or + STORE command, as well as by unilateral server decision (e.g., + flag updates). + + The current data items are: + + BODY + A form of BODYSTRUCTURE without extension data. + + BODY[<section>]<<origin octet>> + A string expressing the body contents of the specified section. + The string SHOULD be interpreted by the client according to the + content transfer encoding, body type, and subtype. + + If the origin octet is specified, this string is a substring of + the entire body contents, starting at that origin octet. This + means that BODY[]<0> MAY be truncated, but BODY[] is NEVER + truncated. + + Note: The origin octet facility MUST NOT be used by a server + in a FETCH response unless the client specifically requested + it by means of a FETCH of a BODY[<section>]<<partial>> data + item. + + 8-bit textual data is permitted if a [CHARSET] identifier is + part of the body parameter parenthesized list for this section. + Note that headers (part specifiers HEADER or MIME, or the + header portion of a MESSAGE/RFC822 part), MUST be 7-bit; 8-bit + characters are not permitted in headers. Note also that the + [_R_F_C_-_2_8_2_2] delimiting blank line between the header and the + body is not affected by header line subsetting; the blank line + is always included as part of header data, except in the case + of a message which has no body and no blank line. + + Non-textual data such as binary data MUST be transfer encoded + into a textual form, such as BASE64, prior to being sent to the + client. To derive the original binary data, the client MUST + decode the transfer encoded string. + + BODYSTRUCTURE + A parenthesized list that describes the [MIME-IMB] body + structure of a message. This is computed by the server by + parsing the [MIME-IMB] header fields, defaulting various fields + as necessary. + + For example, a simple text message of 48 lines and 2279 octets + can have a body structure of: ("TEXT" "PLAIN" ("CHARSET" + "US-ASCII") NIL NIL "7BIT" 2279 48) + + Multiple parts are indicated by parenthesis nesting. Instead + of a body type as the first element of the parenthesized list, + there is a sequence of one or more nested body structures. The + second element of the parenthesized list is the multipart + subtype (mixed, digest, parallel, alternative, etc.). + + For example, a two part message consisting of a text and a + BASE64-encoded text attachment can have a body structure of: + (("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152 + 23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff") + "<_9_6_0_7_2_3_1_6_3_4_0_7_._2_0_1_1_7_h_@_c_a_c_._w_a_s_h_i_n_g_t_o_n_._e_d_u>" "Compiler diff" + "BASE64" 4554 73) "MIXED") + + Extension data follows the multipart subtype. Extension data + is never returned with the BODY fetch, but can be returned with + a BODYSTRUCTURE fetch. Extension data, if present, MUST be in + the defined order. The extension data of a multipart body part + are in the following order: + + body parameter parenthesized list + A parenthesized list of attribute/value pairs [e.g., ("foo" + "bar" "baz" "rag") where "bar" is the value of "foo", and + "rag" is the value of "baz"] as defined in [MIME-IMB]. + + body disposition + A parenthesized list, consisting of a disposition type + string, followed by a parenthesized list of disposition + attribute/value pairs as defined in [DISPOSITION]. + + body language + A string or parenthesized list giving the body language + value as defined in [LANGUAGE-TAGS]. + + body location + A string list giving the body content URI as defined in + [LOCATION]. + + Any following extension data are not yet defined in this + version of the protocol. Such extension data can consist of + zero or more NILs, strings, numbers, or potentially nested + parenthesized lists of such data. Client implementations that + do a BODYSTRUCTURE fetch MUST be prepared to accept such + extension data. Server implementations MUST NOT send such + extension data until it has been defined by a revision of this + protocol. + + The basic fields of a non-multipart body part are in the + following order: + + body type + A string giving the content media type name as defined in + [MIME-IMB]. + + body subtype + A string giving the content subtype name as defined in + [MIME-IMB]. + + body parameter parenthesized list + A parenthesized list of attribute/value pairs [e.g., ("foo" + "bar" "baz" "rag") where "bar" is the value of "foo" and + "rag" is the value of "baz"] as defined in [MIME-IMB]. + + body id + A string giving the content id as defined in [MIME-IMB]. + + body description + A string giving the content description as defined in + [MIME-IMB]. + + body encoding + A string giving the content transfer encoding as defined in + [MIME-IMB]. + + body size + A number giving the size of the body in octets. Note that + this size is the size in its transfer encoding and not the + resulting size after any decoding. + + A body type of type MESSAGE and subtype _R_F_C_8_2_2 contains, + immediately after the basic fields, the envelope structure, + body structure, and size in text lines of the encapsulated + message. + + A body type of type TEXT contains, immediately after the basic + fields, the size of the body in text lines. Note that this + size is the size in its content transfer encoding and not the + resulting size after any decoding. + + Extension data follows the basic fields and the type-specific + fields listed above. Extension data is never returned with the + BODY fetch, but can be returned with a BODYSTRUCTURE fetch. + Extension data, if present, MUST be in the defined order. + + The extension data of a non-multipart body part are in the + following order: + + body MD5 + A string giving the body MD5 value as defined in [MD5]. + + body disposition + A parenthesized list with the same content and function as + the body disposition for a multipart body part. + + body language + A string or parenthesized list giving the body language + value as defined in [LANGUAGE-TAGS]. + + body location + A string list giving the body content URI as defined in + [LOCATION]. + + Any following extension data are not yet defined in this + version of the protocol, and would be as described above under + multipart extension data. + + ENVELOPE + A parenthesized list that describes the envelope structure of a + message. This is computed by the server by parsing the + [_R_F_C_-_2_8_2_2] header into the component parts, defaulting various + fields as necessary. + + The fields of the envelope structure are in the following + order: date, subject, from, sender, reply-to, to, cc, bcc, + in-reply-to, and message-id. The date, subject, in-reply-to, + and message-id fields are strings. The from, sender, reply-to, + to, cc, and bcc fields are parenthesized lists of address + structures. + + An address structure is a parenthesized list that describes an + electronic mail address. The fields of an address structure + are in the following order: personal name, [SMTP] + at-domain-list (source route), mailbox name, and host name. + + [_R_F_C_-_2_8_2_2] group syntax is indicated by a special form of + address structure in which the host name field is NIL. If the + mailbox name field is also NIL, this is an end of group marker + (semi-colon in _R_F_C_ _8_2_2 syntax). If the mailbox name field is + non-NIL, this is a start of group marker, and the mailbox name + field holds the group name phrase. + + If the Date, Subject, In-Reply-To, and Message-ID header lines + are absent in the [_R_F_C_-_2_8_2_2] header, the corresponding member + of the envelope is NIL; if these header lines are present but + empty the corresponding member of the envelope is the empty + string. + + Note: some servers may return a NIL envelope member in the + "present but empty" case. Clients SHOULD treat NIL and + empty string as identical. + + Note: [_R_F_C_-_2_8_2_2] requires that all messages have a valid + Date header. Therefore, the date member in the envelope can + not be NIL or the empty string. + + Note: [_R_F_C_-_2_8_2_2] requires that the In-Reply-To and + Message-ID headers, if present, have non-empty content. + Therefore, the in-reply-to and message-id members in the + envelope can not be the empty string. + + If the From, To, cc, and bcc header lines are absent in the + [_R_F_C_-_2_8_2_2] header, or are present but empty, the corresponding + member of the envelope is NIL. + + If the Sender or Reply-To lines are absent in the [_R_F_C_-_2_8_2_2] + header, or are present but empty, the server sets the + corresponding member of the envelope to be the same value as + the from member (the client is not expected to know to do + this). + + Note: [_R_F_C_-_2_8_2_2] requires that all messages have a valid + From header. Therefore, the from, sender, and reply-to + members in the envelope can not be NIL. + + FLAGS + A parenthesized list of flags that are set for this message. + + INTERNALDATE + A string representing the internal date of the message. + + _R_F_C_8_2_2 + Equivalent to BODY[]. + + _R_F_C_8_2_2.HEADER + Equivalent to BODY[HEADER]. Note that this did not result in + \Seen being set, because _R_F_C_8_2_2.HEADER response data occurs as + a result of a FETCH of _R_F_C_8_2_2.HEADER. BODY[HEADER] response + data occurs as a result of a FETCH of BODY[HEADER] (which sets + \Seen) or BODY.PEEK[HEADER] (which does not set \Seen). + + _R_F_C_8_2_2.SIZE + A number expressing the [_R_F_C_-_2_8_2_2] size of the message. + + _R_F_C_8_2_2.TEXT + Equivalent to BODY[TEXT]. + + UID + A number expressing the unique identifier of the message. + + Example: S: * 23 FETCH (FLAGS (\Seen) _R_F_C_8_2_2.SIZE 44827) + +7.5. Server Responses - Command Continuation Request + + The command continuation request response is indicated by a "+" token + instead of a tag. This form of response indicates that the server is + ready to accept the continuation of a command from the client. The + remainder of this response is a line of text. + + This response is used in the AUTHENTICATE command to transmit server + data to the client, and request additional client data. This + response is also used if an argument to any command is a literal. + + The client is not permitted to send the octets of the literal unless + the server indicates that it is expected. This permits the server to + process commands and reject errors on a line-by-line basis. The + remainder of the command, including the CRLF that terminates a + command, follows the octets of the literal. If there are any + additional command arguments, the literal octets are followed by a + space and those arguments. + + Example: C: A001 LOGIN {11} + S: + Ready for additional command text + C: FRED FOOBAR {7} + S: + Ready for additional command text + C: fat man + S: A001 OK LOGIN completed + C: A044 BLURDYBLOOP {102856} + S: A044 BAD No such command as "BLURDYBLOOP" + +8. Sample IMAP4rev1 connection + + The following is a transcript of an IMAP4rev1 connection. A long + line in this sample is broken for editorial clarity. + +S: * OK IMAP4rev1 Service Ready +C: a001 login mrc secret +S: a001 OK LOGIN completed +C: a002 select inbox +S: * 18 EXISTS +S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) +S: * 2 RECENT +S: * OK [UNSEEN 17] Message 17 is the first unseen message +S: * OK [UIDVALIDITY 3857529045] UIDs valid +S: a002 OK [READ-WRITE] SELECT completed +C: a003 fetch 12 full +S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700" + _R_F_C_8_2_2.SIZE 4286 ENVELOPE ("Wed, 17 Jul 1996 02:23:25 -0700 (PDT)" + "IMAP4rev1 WG mtg summary and minutes" + (("Terry Gray" NIL "gray" "cac.washington.edu")) + (("Terry Gray" NIL "gray" "cac.washington.edu")) + (("Terry Gray" NIL "gray" "cac.washington.edu")) + ((NIL NIL "imap" "cac.washington.edu")) + ((NIL NIL "minutes" "CNRI.Reston.VA.US") + ("John Klensin" NIL "KLENSIN" "MIT.EDU")) NIL NIL + "<_B_2_7_3_9_7_-_0_1_0_0_0_0_0_@_c_a_c_._w_a_s_h_i_n_g_t_o_n_._e_d_u>") + BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028 + 92)) +S: a003 OK FETCH completed +C: a004 fetch 12 body[header] +S: * 12 FETCH (BODY[HEADER] {342} +S: Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT) +S: From: Terry Gray <_g_r_a_y_@_c_a_c_._w_a_s_h_i_n_g_t_o_n_._e_d_u> +S: Subject: IMAP4rev1 WG mtg summary and minutes +S: To: _i_m_a_p_@_c_a_c_._w_a_s_h_i_n_g_t_o_n_._e_d_u +S: cc: _m_i_n_u_t_e_s_@_C_N_R_I_._R_e_s_t_o_n_._V_A_._U_S, John Klensin <_K_L_E_N_S_I_N_@_M_I_T_._E_D_U> +S: Message-Id: <B27397-0100000@cac.washington.edu> +S: MIME-Version: 1.0 +S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII +S: +S: ) +S: a004 OK FETCH completed +C: a005 store 12 +flags \deleted +S: * 12 FETCH (FLAGS (\Seen \Deleted)) +S: a005 OK +FLAGS completed +C: a006 logout +S: * BYE IMAP4rev1 server terminating connection +S: a006 OK LOGOUT completed + +9. Formal Syntax + + The following syntax specification uses the Augmented Backus-Naur + Form (ABNF) notation as specified in [ABNF]. + + In the case of alternative or optional rules in which a later rule + overlaps an earlier rule, the rule which is listed earlier MUST take + priority. For example, "\Seen" when parsed as a flag is the \Seen + flag name and not a flag-extension, even though "\Seen" can be parsed + as a flag-extension. Some, but not all, instances of this rule are + noted below. + + Note: [ABNF] rules MUST be followed strictly; in + particular: + + (1) Except as noted otherwise, all alphabetic characters + are case-insensitive. The use of upper or lower case + characters to define token strings is for editorial clarity + only. Implementations MUST accept these strings in a + case-insensitive fashion. + + (2) In all cases, SP refers to exactly one space. It is + NOT permitted to substitute TAB, insert additional spaces, + or otherwise treat SP as being equivalent to LWSP. + + (3) The ASCII NUL character, %x00, MUST NOT be used at any + time. + +address = "(" addr-name SP addr-adl SP addr-mailbox SP + addr-host ")" + +addr-adl = nstring + ; Holds route from [_R_F_C_-_2_8_2_2] route-addr if + ; non-NIL + +addr-host = nstring + ; NIL indicates [_R_F_C_-_2_8_2_2] group syntax. + ; Otherwise, holds [_R_F_C_-_2_8_2_2] domain name + +addr-mailbox = nstring + ; NIL indicates end of [_R_F_C_-_2_8_2_2] group; if + ; non-NIL and addr-host is NIL, holds + ; [_R_F_C_-_2_8_2_2] group name. + ; Otherwise, holds [_R_F_C_-_2_8_2_2] local-part + ; after removing [_R_F_C_-_2_8_2_2] quoting + +addr-name = nstring + ; If non-NIL, holds phrase from [_R_F_C_-_2_8_2_2] + ; mailbox after removing [_R_F_C_-_2_8_2_2] quoting + +append = "APPEND" SP mailbox [SP flag-list] [SP date-time] SP + literal + +astring = 1*ASTRING-CHAR / string + +ASTRING-CHAR = ATOM-CHAR / resp-specials + +atom = 1*ATOM-CHAR + +ATOM-CHAR = <any CHAR except atom-specials> + +atom-specials = "(" / ")" / "{" / SP / CTL / list-wildcards / + quoted-specials / resp-specials + +authenticate = "AUTHENTICATE" SP auth-type *(CRLF base64) + +auth-type = atom + ; Defined by [SASL] + +base64 = *(4base64-char) [base64-terminal] + +base64-char = ALPHA / DIGIT / "+" / "/" + ; Case-sensitive + +base64-terminal = (2base64-char "==") / (3base64-char "=") + +body = "(" (body-type-1part / body-type-mpart) ")" + +body-extension = nstring / number / + "(" body-extension *(SP body-extension) ")" + ; Future expansion. Client implementations + ; MUST accept body-extension fields. Server + ; implementations MUST NOT generate + ; body-extension fields except as defined by + ; future standard or standards-track + ; revisions of this specification. + +body-ext-1part = body-fld-md5 [SP body-fld-dsp [SP body-fld-lang + [SP body-fld-loc *(SP body-extension)]]] + ; MUST NOT be returned on non-extensible + ; "BODY" fetch + +body-ext-mpart = body-fld-param [SP body-fld-dsp [SP body-fld-lang + [SP body-fld-loc *(SP body-extension)]]] + ; MUST NOT be returned on non-extensible + ; "BODY" fetch + +body-fields = body-fld-param SP body-fld-id SP body-fld-desc SP + body-fld-enc SP body-fld-octets + +body-fld-desc = nstring + +body-fld-dsp = "(" string SP body-fld-param ")" / nil + +body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/ + "QUOTED-PRINTABLE") DQUOTE) / string + +body-fld-id = nstring + +body-fld-lang = nstring / "(" string *(SP string) ")" + +body-fld-loc = nstring + +body-fld-lines = number + +body-fld-md5 = nstring + +body-fld-octets = number + +body-fld-param = "(" string SP string *(SP string SP string) ")" / nil + +body-type-1part = (body-type-basic / body-type-msg / body-type-text) + [SP body-ext-1part] + +body-type-basic = media-basic SP body-fields + ; MESSAGE subtype MUST NOT be "_R_F_C_8_2_2" + +body-type-mpart = 1*body SP media-subtype + [SP body-ext-mpart] + +body-type-msg = media-message SP body-fields SP envelope + SP body SP body-fld-lines + +body-type-text = media-text SP body-fields SP body-fld-lines + +capability = ("AUTH=" auth-type) / atom + ; New capabilities MUST begin with "X" or be + ; registered with IANA as standard or + ; standards-track + +capability-data = "CAPABILITY" *(SP capability) SP "IMAP4rev1" + *(SP capability) + ; Servers MUST implement the STARTTLS, AUTH=PLAIN, + ; and LOGINDISABLED capabilities + ; Servers which offer _R_F_C_ _1_7_3_0 compatibility MUST + ; list "IMAP4" as the first capability. + +CHAR8 = %x01-ff + ; any OCTET except NUL, %x00 + +command = tag SP (command-any / command-auth / command-nonauth / + command-select) CRLF + ; Modal based on state + +command-any = "CAPABILITY" / "LOGOUT" / "NOOP" / x-command + ; Valid in all states + +command-auth = append / create / delete / examine / list / lsub / + rename / select / status / subscribe / unsubscribe + ; Valid only in Authenticated or Selected state + +command-nonauth = login / authenticate / "STARTTLS" + ; Valid only when in Not Authenticated state + +command-select = "CHECK" / "CLOSE" / "EXPUNGE" / copy / fetch / store / + uid / search + ; Valid only when in Selected state + +continue-req = "+" SP (resp-text / base64) CRLF + +copy = "COPY" SP sequence-set SP mailbox + +create = "CREATE" SP mailbox + ; Use of INBOX gives a NO error + +date = date-text / DQUOTE date-text DQUOTE + +date-day = 1*2DIGIT + ; Day of month + +date-day-fixed = (SP DIGIT) / 2DIGIT + ; Fixed-format version of date-day + +date-month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" / + "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec" + +date-text = date-day "-" date-month "-" date-year + +date-year = 4DIGIT + +date-time = DQUOTE date-day-fixed "-" date-month "-" date-year + SP time SP zone DQUOTE + +delete = "DELETE" SP mailbox + ; Use of INBOX gives a NO error + +digit-nz = %x31-39 + ; 1-9 + +envelope = "(" env-date SP env-subject SP env-from SP + env-sender SP env-reply-to SP env-to SP env-cc SP + env-bcc SP env-in-reply-to SP env-message-id ")" + +env-bcc = "(" 1*address ")" / nil + +env-cc = "(" 1*address ")" / nil + +env-date = nstring + +env-from = "(" 1*address ")" / nil + +env-in-reply-to = nstring + +env-message-id = nstring + +env-reply-to = "(" 1*address ")" / nil + +env-sender = "(" 1*address ")" / nil + +env-subject = nstring + +env-to = "(" 1*address ")" / nil + +examine = "EXAMINE" SP mailbox + +fetch = "FETCH" SP sequence-set SP ("ALL" / "FULL" / "FAST" / + fetch-att / "(" fetch-att *(SP fetch-att) ")") + +fetch-att = "ENVELOPE" / "FLAGS" / "INTERNALDATE" / + "_R_F_C_8_2_2" [".HEADER" / ".SIZE" / ".TEXT"] / + "BODY" ["STRUCTURE"] / "UID" / + "BODY" section ["<" number "." nz-number ">"] / + "BODY.PEEK" section ["<" number "." nz-number ">"] + +flag = "\Answered" / "\Flagged" / "\Deleted" / + "\Seen" / "\Draft" / flag-keyword / flag-extension + ; Does not include "\Recent" + +flag-extension = "\" atom + ; Future expansion. Client implementations + ; MUST accept flag-extension flags. Server + ; implementations MUST NOT generate + ; flag-extension flags except as defined by + ; future standard or standards-track + ; revisions of this specification. + +flag-fetch = flag / "\Recent" + +flag-keyword = atom + +flag-list = "(" [flag *(SP flag)] ")" + +flag-perm = flag / "\*" + +greeting = "*" SP (resp-cond-auth / resp-cond-bye) CRLF + +header-fld-name = astring + +header-list = "(" header-fld-name *(SP header-fld-name) ")" + +list = "LIST" SP mailbox SP list-mailbox + +list-mailbox = 1*list-char / string + +list-char = ATOM-CHAR / list-wildcards / resp-specials + +list-wildcards = "%" / "*" + +literal = "{" number "}" CRLF *CHAR8 + ; Number represents the number of CHAR8s + +login = "LOGIN" SP userid SP password + +lsub = "LSUB" SP mailbox SP list-mailbox + +mailbox = "INBOX" / astring + ; INBOX is case-insensitive. All case variants of + ; INBOX (e.g., "iNbOx") MUST be interpreted as INBOX + ; not as an astring. An astring which consists of + ; the case-insensitive sequence "I" "N" "B" "O" "X" + ; is considered to be INBOX and not an astring. + ; Refer to section 5.1 for further + ; semantic details of mailbox names. + +mailbox-data = "FLAGS" SP flag-list / "LIST" SP mailbox-list / + "LSUB" SP mailbox-list / "SEARCH" *(SP nz-number) / + "STATUS" SP mailbox SP "(" [status-att-list] ")" / + number SP "EXISTS" / number SP "RECENT" + +mailbox-list = "(" [mbx-list-flags] ")" SP + (DQUOTE QUOTED-CHAR DQUOTE / nil) SP mailbox + +mbx-list-flags = *(mbx-list-oflag SP) mbx-list-sflag + *(SP mbx-list-oflag) / + mbx-list-oflag *(SP mbx-list-oflag) + +mbx-list-oflag = "\Noinferiors" / flag-extension + ; Other flags; multiple possible per LIST response + +mbx-list-sflag = "\Noselect" / "\Marked" / "\Unmarked" + ; Selectability flags; only one per LIST response + +media-basic = ((DQUOTE ("APPLICATION" / "AUDIO" / "IMAGE" / + "MESSAGE" / "VIDEO") DQUOTE) / string) SP + media-subtype + ; Defined in [MIME-IMT] + +media-message = DQUOTE "MESSAGE" DQUOTE SP DQUOTE "_R_F_C_8_2_2" DQUOTE + ; Defined in [MIME-IMT] + +media-subtype = string + ; Defined in [MIME-IMT] + +media-text = DQUOTE "TEXT" DQUOTE SP media-subtype + ; Defined in [MIME-IMT] + +message-data = nz-number SP ("EXPUNGE" / ("FETCH" SP msg-att)) + +msg-att = "(" (msg-att-dynamic / msg-att-static) + *(SP (msg-att-dynamic / msg-att-static)) ")" + +msg-att-dynamic = "FLAGS" SP "(" [flag-fetch *(SP flag-fetch)] ")" + ; MAY change for a message + +msg-att-static = "ENVELOPE" SP envelope / "INTERNALDATE" SP date-time / + "_R_F_C_8_2_2" [".HEADER" / ".TEXT"] SP nstring / + "_R_F_C_8_2_2.SIZE" SP number / + "BODY" ["STRUCTURE"] SP body / + "BODY" section ["<" number ">"] SP nstring / + "UID" SP uniqueid + ; MUST NOT change for a message + +nil = "NIL" + +nstring = string / nil + +number = 1*DIGIT + ; Unsigned 32-bit integer + ; (0 <= n < 4,294,967,296) + +nz-number = digit-nz *DIGIT + ; Non-zero unsigned 32-bit integer + ; (0 < n < 4,294,967,296) + +password = astring + +quoted = DQUOTE *QUOTED-CHAR DQUOTE + +QUOTED-CHAR = <any TEXT-CHAR except quoted-specials> / + "\" quoted-specials + +quoted-specials = DQUOTE / "\" + +rename = "RENAME" SP mailbox SP mailbox + ; Use of INBOX as a destination gives a NO error + +response = *(continue-req / response-data) response-done + +response-data = "*" SP (resp-cond-state / resp-cond-bye / + mailbox-data / message-data / capability-data) CRLF + +response-done = response-tagged / response-fatal + +response-fatal = "*" SP resp-cond-bye CRLF + ; Server closes connection immediately + +response-tagged = tag SP resp-cond-state CRLF + +resp-cond-auth = ("OK" / "PREAUTH") SP resp-text + ; Authentication condition + +resp-cond-bye = "BYE" SP resp-text + +resp-cond-state = ("OK" / "NO" / "BAD") SP resp-text + ; Status condition + +resp-specials = "]" + +resp-text = ["[" resp-text-code "]" SP] text + +resp-text-code = "ALERT" / + "BADCHARSET" [SP "(" astring *(SP astring) ")" ] / + capability-data / "PARSE" / + "PERMANENTFLAGS" SP "(" + [flag-perm *(SP flag-perm)] ")" / + "READ-ONLY" / "READ-WRITE" / "TRYCREATE" / + "UIDNEXT" SP nz-number / "UIDVALIDITY" SP nz-number / + "UNSEEN" SP nz-number / + atom [SP 1*<any TEXT-CHAR except "]">] + +search = "SEARCH" [SP "CHARSET" SP astring] 1*(SP search-key) + ; CHARSET argument to MUST be registered with IANA + +search-key = "ALL" / "ANSWERED" / "BCC" SP astring / + "BEFORE" SP date / "BODY" SP astring / + "CC" SP astring / "DELETED" / "FLAGGED" / + "FROM" SP astring / "KEYWORD" SP flag-keyword / + "NEW" / "OLD" / "ON" SP date / "RECENT" / "SEEN" / + "SINCE" SP date / "SUBJECT" SP astring / + "TEXT" SP astring / "TO" SP astring / + "UNANSWERED" / "UNDELETED" / "UNFLAGGED" / + "UNKEYWORD" SP flag-keyword / "UNSEEN" / + ; Above this line were in [IMAP2] + "DRAFT" / "HEADER" SP header-fld-name SP astring / + "LARGER" SP number / "NOT" SP search-key / + "OR" SP search-key SP search-key / + "SENTBEFORE" SP date / "SENTON" SP date / + "SENTSINCE" SP date / "SMALLER" SP number / + "UID" SP sequence-set / "UNDRAFT" / sequence-set / + "(" search-key *(SP search-key) ")" + +section = "[" [section-spec] "]" + +section-msgtext = "HEADER" / "HEADER.FIELDS" [".NOT"] SP header-list / + "TEXT" + ; top-level or MESSAGE/RFC822 part + +section-part = nz-number *("." nz-number) + ; body part nesting + +section-spec = section-msgtext / (section-part ["." section-text]) + +section-text = section-msgtext / "MIME" + ; text other than actual body part (headers, etc.) + +select = "SELECT" SP mailbox + +seq-number = nz-number / "*" + ; message sequence number (COPY, FETCH, STORE + ; commands) or unique identifier (UID COPY, + ; UID FETCH, UID STORE commands). + ; * represents the largest number in use. In + ; the case of message sequence numbers, it is + ; the number of messages in a non-empty mailbox. + ; In the case of unique identifiers, it is the + ; unique identifier of the last message in the + ; mailbox or, if the mailbox is empty, the + ; mailbox's current UIDNEXT value. + ; The server should respond with a tagged BAD + ; response to a command that uses a message + ; sequence number greater than the number of + ; messages in the selected mailbox. This + ; includes "*" if the selected mailbox is empty. + +seq-range = seq-number ":" seq-number + ; two seq-number values and all values between + ; these two regardless of order. + ; Example: 2:4 and 4:2 are equivalent and indicate + ; values 2, 3, and 4. + ; Example: a unique identifier sequence range of + ; 3291:* includes the UID of the last message in + ; the mailbox, even if that value is less than 3291. + +sequence-set = (seq-number / seq-range) *("," sequence-set) + ; set of seq-number values, regardless of order. + ; Servers MAY coalesce overlaps and/or execute the + ; sequence in any order. + ; Example: a message sequence number set of + ; 2,4:7,9,12:* for a mailbox with 15 messages is + ; equivalent to 2,4,5,6,7,9,12,13,14,15 + ; Example: a message sequence number set of *:4,5:7 + ; for a mailbox with 10 messages is equivalent to + ; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and + ; overlap coalesced to be 4,5,6,7,8,9,10. + +status = "STATUS" SP mailbox SP + "(" status-att *(SP status-att) ")" + +status-att = "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" / + "UNSEEN" + +status-att-list = status-att SP number *(SP status-att SP number) + +store = "STORE" SP sequence-set SP store-att-flags + +store-att-flags = (["+" / "-"] "FLAGS" [".SILENT"]) SP + (flag-list / (flag *(SP flag))) + +string = quoted / literal + +subscribe = "SUBSCRIBE" SP mailbox + +tag = 1*<any ASTRING-CHAR except "+"> + +text = 1*TEXT-CHAR + +TEXT-CHAR = <any CHAR except CR and LF> + +time = 2DIGIT ":" 2DIGIT ":" 2DIGIT + ; Hours minutes seconds + +uid = "UID" SP (copy / fetch / search / store) + ; Unique identifiers used instead of message + ; sequence numbers + +uniqueid = nz-number + ; Strictly ascending + +unsubscribe = "UNSUBSCRIBE" SP mailbox + +userid = astring + +x-command = "X" atom <experimental command arguments> + +zone = ("+" / "-") 4DIGIT + ; Signed four-digit value of hhmm representing + ; hours and minutes east of Greenwich (that is, + ; the amount that the given time differs from + ; Universal Time). Subtracting the timezone + ; from the given time will give the UT form. + ; The Universal Time zone is "+0000". + +10. Author's Note + + This document is a revision or rewrite of earlier documents, and + supercedes the protocol specification in those documents: _R_F_C_ _2_0_6_0, + _R_F_C_ _1_7_3_0, unpublished IMAP2bis.TXT document, _R_F_C_ _1_1_7_6, and _R_F_C_ _1_0_6_4. + +11. Security Considerations + + IMAP4rev1 protocol transactions, including electronic mail data, are + sent in the clear over the network unless protection from snooping is + negotiated. This can be accomplished either by the use of STARTTLS, + negotiated privacy protection in the AUTHENTICATE command, or some + other protection mechanism. + +11.1. STARTTLS Security Considerations + + The specification of the STARTTLS command and LOGINDISABLED + capability in this document replaces that in [IMAP-TLS]. [IMAP-TLS] + remains normative for the PLAIN [SASL] authenticator. + + IMAP client and server implementations MUST implement the + TLS_RSA_WITH_RC4_128_MD5 [TLS] cipher suite, and SHOULD implement the + TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA [TLS] cipher suite. This is + important as it assures that any two compliant implementations can be + configured to interoperate. All other cipher suites are OPTIONAL. + Note that this is a change from section 2.1 of [IMAP-TLS]. + + During the [TLS] negotiation, the client MUST check its understanding + of the server hostname against the server's identity as presented in + the server Certificate message, in order to prevent man-in-the-middle + attacks. If the match fails, the client SHOULD either ask for + explicit user confirmation, or terminate the connection and indicate + that the server's identity is suspect. Matching is performed + according to these rules: + + The client MUST use the server hostname it used to open the + connection as the value to compare against the server name + as expressed in the server certificate. The client MUST + NOT use any form of the server hostname derived from an + insecure remote source (e.g., insecure DNS lookup). CNAME + canonicalization is not done. + + If a subjectAltName extension of type dNSName is present in + the certificate, it SHOULD be used as the source of the + server's identity. + + Matching is case-insensitive. + + A "*" wildcard character MAY be used as the left-most name + component in the certificate. For example, *.example.com + would match a.example.com, foo.example.com, etc. but would + not match example.com. + + If the certificate contains multiple names (e.g., more than + one dNSName field), then a match with any one of the fields + is considered acceptable. + + Both the client and server MUST check the result of the STARTTLS + command and subsequent [TLS] negotiation to see whether acceptable + authentication or privacy was achieved. + +11.2. Other Security Considerations + + A server error message for an AUTHENTICATE command which fails due to + invalid credentials SHOULD NOT detail why the credentials are + invalid. + + Use of the LOGIN command sends passwords in the clear. This can be + avoided by using the AUTHENTICATE command with a [SASL] mechanism + that does not use plaintext passwords, by first negotiating + encryption via STARTTLS or some other protection mechanism. + + A server implementation MUST implement a configuration that, at the + time of authentication, requires: + (1) The STARTTLS command has been negotiated. + OR + (2) Some other mechanism that protects the session from password + snooping has been provided. + OR + (3) The following measures are in place: + (a) The LOGINDISABLED capability is advertised, and [SASL] + mechanisms (such as PLAIN) using plaintext passwords are NOT + advertised in the CAPABILITY list. + AND + (b) The LOGIN command returns an error even if the password is + correct. + AND + (c) The AUTHENTICATE command returns an error with all [SASL] + mechanisms that use plaintext passwords, even if the password + is correct. + + A server error message for a failing LOGIN command SHOULD NOT specify + that the user name, as opposed to the password, is invalid. + + A server SHOULD have mechanisms in place to limit or delay failed + AUTHENTICATE/LOGIN attempts. + + Additional security considerations are discussed in the section + discussing the AUTHENTICATE and LOGIN commands. + +12. IANA Considerations + + IMAP4 capabilities are registered by publishing a standards track or + IESG approved experimental RFC. The registry is currently located + at: + + _h_t_t_p_:_/_/_w_w_w_._i_a_n_a_._o_r_g_/_a_s_s_i_g_n_m_e_n_t_s_/_i_m_a_p_4_-_c_a_p_a_b_i_l_i_t_i_e_s + + As this specification revises the STARTTLS and LOGINDISABLED + extensions previously defined in [IMAP-TLS], the registry will be + updated accordingly. + +Appendices + +A. Normative References + + The following documents contain definitions or specifications that + are necessary to understand this document properly: + [ABNF] Crocker, D. and P. Overell, "Augmented BNF for + Syntax Specifications: ABNF", _R_F_C_ _2_2_3_4, + November 1997. + + [ANONYMOUS] Newman, C., "Anonymous SASL Mechanism", RFC + 2245, November 1997. + + [CHARSET] Freed, N. and J. Postel, "IANA Character Set + Registration Procedures", _R_F_C_ _2_9_7_8, October + 2000. + + [DIGEST-MD5] Leach, P. and C. Newman, "Using Digest + Authentication as a SASL Mechanism", _R_F_C_ _2_8_3_1, + May 2000. + + [DISPOSITION] Troost, R., Dorner, S. and K. Moore, + "Communicating Presentation Information in + Internet Messages: The Content-Disposition + Header", _R_F_C_ _2_1_8_3, August 1997. + + [IMAP-TLS] Newman, C., "Using TLS with IMAP, POP3 and + ACAP", _R_F_C_ _2_5_9_5, June 1999. + + [KEYWORDS] Bradner, S., "Key words for use in RFCs to + Indicate Requirement Levels", BCP 14, _R_F_C_ _2_1_1_9, + March 1997. + + [LANGUAGE-TAGS] Alvestrand, H., "Tags for the Identification of + Languages", BCP 47, _R_F_C_ _3_0_6_6, January 2001. + + [LOCATION] Palme, J., Hopmann, A. and N. Shelness, "MIME + Encapsulation of Aggregate Documents, such as + HTML (MHTML)", _R_F_C_ _2_5_5_7, March 1999. + + [MD5] Myers, J. and M. Rose, "The Content-MD5 Header + Field", _R_F_C_ _1_8_6_4, October 1995. + + [MIME-HDRS] Moore, K., "MIME (Multipurpose Internet Mail + Extensions) Part Three: Message Header + Extensions for Non-ASCII Text", _R_F_C_ _2_0_4_7, + November 1996. + + [MIME-IMB] Freed, N. and N. Borenstein, "MIME + (Multipurpose Internet Mail Extensions) Part + One: Format of Internet Message Bodies", RFC + 2045, November 1996. + + [MIME-IMT] Freed, N. and N. Borenstein, "MIME + (Multipurpose Internet Mail Extensions) Part + Two: Media Types", _R_F_C_ _2_0_4_6, November 1996. + + [_R_F_C_-_2_8_2_2] Resnick, P., "Internet Message Format", RFC + 2822, April 2001. + + [SASL] Myers, J., "Simple Authentication and Security + Layer (SASL)", _R_F_C_ _2_2_2_2, October 1997. + + [TLS] Dierks, T. and C. Allen, "The TLS Protocol + Version 1.0", _R_F_C_ _2_2_4_6, January 1999. + + [UTF-7] Goldsmith, D. and M. Davis, "UTF-7: A Mail-Safe + Transformation Format of Unicode", _R_F_C_ _2_1_5_2, + May 1997. + + The following documents describe quality-of-implementation issues + that should be carefully considered when implementing this protocol: + + [IMAP-IMPLEMENTATION] Leiba, B., "IMAP Implementation + Recommendations", _R_F_C_ _2_6_8_3, September 1999. + + [IMAP-MULTIACCESS] Gahrns, M., "IMAP4 Multi-Accessed Mailbox + Practice", _R_F_C_ _2_1_8_0, July 1997. + +A.1 Informative References + + The following documents describe related protocols: + + [IMAP-DISC] Austein, R., "Synchronization Operations for + Disconnected IMAP4 Clients", Work in Progress. + + [IMAP-MODEL] Crispin, M., "Distributed Electronic Mail + Models in IMAP4", _R_F_C_ _1_7_3_3, December 1994. + + [ACAP] Newman, C. and J. Myers, "ACAP -- Application + Configuration Access Protocol", _R_F_C_ _2_2_4_4, + November 1997. + + [SMTP] Klensin, J., "Simple Mail Transfer Protocol", + STD 10, _R_F_C_ _2_8_2_1, April 2001. + + The following documents are historical or describe historical aspects + of this protocol: + + [IMAP-COMPAT] Crispin, M., "IMAP4 Compatibility with + IMAP2bis", _R_F_C_ _2_0_6_1, December 1996. + + [IMAP-HISTORICAL] Crispin, M., "IMAP4 Compatibility with IMAP2 + and IMAP2bis", _R_F_C_ _1_7_3_2, December 1994. + + [IMAP-OBSOLETE] Crispin, M., "Internet Message Access Protocol + - Obsolete Syntax", _R_F_C_ _2_0_6_2, December 1996. + + [IMAP2] Crispin, M., "Interactive Mail Access Protocol + - Version 2", _R_F_C_ _1_1_7_6, August 1990. + + [_R_F_C_-_8_2_2] Crocker, D., "Standard for the Format of ARPA + Internet Text Messages", STD 11, _R_F_C_ _8_2_2, + August 1982. + + [_R_F_C_-_8_2_1] Postel, J., "Simple Mail Transfer Protocol", + STD 10, _R_F_C_ _8_2_1, August 1982. + +B. Changes from _R_F_C_ _2_0_6_0 + + 1) Clarify description of unique identifiers and their semantics. + + 2) Fix the SELECT description to clarify that UIDVALIDITY is required + in the SELECT and EXAMINE responses. + + 3) Added an example of a failing search. + + 4) Correct store-att-flags: "#flag" should be "1#flag". + + 5) Made search and section rules clearer. + + 6) Correct the STORE example. + + 7) Correct "BASE645" misspelling. + + 8) Remove extraneous close parenthesis in example of two-part message + with text and BASE64 attachment. + + 9) Remove obsolete "MAILBOX" response from mailbox-data. + + 10) A spurious "<" in the rule for mailbox-data was removed. + + 11) Add CRLF to continue-req. + + 12) Specifically exclude "]" from the atom in resp-text-code. + + 13) Clarify that clients and servers should adhere strictly to the + protocol syntax. + + 14) Emphasize in 5.2 that EXISTS can not be used to shrink a mailbox. + + 15) Add NEWNAME to resp-text-code. + + 16) Clarify that the empty string, not NIL, is used as arguments to + LIST. + + 17) Clarify that NIL can be returned as a hierarchy delimiter for the + empty string mailbox name argument if the mailbox namespace is flat. + + 18) Clarify that addr-mailbox and addr-name have _R_F_C_-_2_8_2_2 quoting + removed. + + 19) Update UTF-7 reference. + + 20) Fix example in 6.3.11. + + 21) Clarify that non-existent UIDs are ignored. + + 22) Update DISPOSITION reference. + + 23) Expand state diagram. + + 24) Clarify that partial fetch responses are only returned in + response to a partial fetch command. + + 25) Add UIDNEXT response code. Correct UIDVALIDITY definition + reference. + + 26) Further clarification of "can" vs. "MAY". + + 27) Reference _R_F_C_-_2_1_1_9. + + 28) Clarify that superfluous shifts are not permitted in modified + UTF-7. + + 29) Clarify that there are no implicit shifts in modified UTF-7. + + 30) Clarify that "INBOX" in a mailbox name is always INBOX, even if + it is given as a string. + + 31) Add missing open parenthesis in media-basic grammar rule. + + 32) Correct attribute syntax in mailbox-data. + + 33) Add UIDNEXT to EXAMINE responses. + + 34) Clarify UNSEEN, PERMANENTFLAGS, UIDVALIDITY, and UIDNEXT + responses in SELECT and EXAMINE. They are required now, but weren't + in older versions. + + 35) Update references with RFC numbers. + + 36) Flush text-mime2. + + 37) Clarify that modified UTF-7 names must be case-sensitive and that + violating the convention should be avoided. + + 38) Correct UID FETCH example. + + 39) Clarify UID FETCH, UID STORE, and UID SEARCH vs. untagged EXPUNGE + responses. + + 40) Clarify the use of the word "convention". + + 41) Clarify that a command is not "in progress" until it has been + fully received (specifically, that a command is not "in progress" + during command continuation negotiation). + + 42) Clarify envelope defaulting. + + 43) Clarify that SP means one and only one space character. + + 44) Forbid silly states in LIST response. + + 45) Clarify that the ENVELOPE, INTERNALDATE, _R_F_C_8_2_2*, BODY*, and UID + for a message is static. + + 46) Add BADCHARSET response code. + + 47) Update formal syntax to [ABNF] conventions. + + 48) Clarify trailing hierarchy delimiter in CREATE semantics. + + 49) Clarify that the "blank line" is the [_R_F_C_-_2_8_2_2] delimiting blank + line. + + 50) Clarify that RENAME should also create hierarchy as needed for + the command to complete. + + 51) Fix body-ext-mpart to not require language if disposition + present. + + 52) Clarify the _R_F_C_8_2_2.HEADER response. + + 53) Correct missing space after charset astring in search. + + 54) Correct missing quote for BADCHARSET in resp-text-code. + + 55) Clarify that ALL, FAST, and FULL preclude any other data items + appearing. + + 56) Clarify semantics of reference argument in LIST. + + 57) Clarify that a null string for SEARCH HEADER X-FOO means any + message with a header line with a field-name of X-FOO regardless of + the text of the header. + + 58) Specifically reserve 8-bit mailbox names for future use as UTF-8. + + 59) It is not an error for the client to store a flag that is not in + the PERMANENTFLAGS list; however, the server will either ignore the + change or make the change in the session only. + + 60) Correct/clarify the text regarding superfluous shifts. + + 61) Correct typographic errors in the "Changes" section. + + 62) Clarify that STATUS must not be used to check for new messages in + the selected mailbox + + 63) Clarify LSUB behavior with "%" wildcard. + + 64) Change AUTHORIZATION to AUTHENTICATE in section 7.5. + + 65) Clarify description of multipart body type. + + 66) Clarify that STORE FLAGS does not affect \Recent. + + 67) Change "west" to "east" in description of timezone. + + 68) Clarify that commands which break command pipelining must wait + for a completion result response. + + 69) Clarify that EXAMINE does not affect \Recent. + + 70) Make description of MIME structure consistent. + + 71) Clarify that date searches disregard the time and timezone of the + INTERNALDATE or Date: header. In other words, "ON 13-APR-2000" means + messages with an INTERNALDATE text which starts with "13-APR-2000", + even if timezone differential from the local timezone is sufficient + to move that INTERNALDATE into the previous or next day. + + 72) Clarify that the header fetches don't add a blank line if one + isn't in the [_R_F_C_-_2_8_2_2] message. + + 73) Clarify (in discussion of UIDs) that messages are immutable. + + 74) Add an example of CHARSET searching. + + 75) Clarify in SEARCH that keywords are a type of flag. + + 76) Clarify the mandatory nature of the SELECT data responses. + + 77) Add optional CAPABILITY response code in the initial OK or + PREAUTH. + + 78) Add note that server can send an untagged CAPABILITY command as + part of the responses to AUTHENTICATE and LOGIN. + + 79) Remove statement about it being unnecessary to issue a CAPABILITY + command more than once in a connection. That statement is no longer + true. + + 80) Clarify that untagged EXPUNGE decrements the number of messages + in the mailbox. + + 81) Fix definition of "body" (concatenation has tighter binding than + alternation). + + 82) Add a new "Special Notes to Implementors" section with reference + to [IMAP-IMPLEMENTATION]. + + 83) Clarify that an untagged CAPABILITY response to an AUTHENTICATE + command should only be done if a security layer was not negotiated. + + 84) Change the definition of atom to exclude "]". Update astring to + include "]" for compatibility with the past. Remove resp-text-atom. + + 85) Remove NEWNAME. It can't work because mailbox names can be + literals and can include "]". Functionality can be addressed via + referrals. + + 86) Move modified UTF-7 rationale in order to have more logical + paragraph flow. + + 87) Clarify UID uniqueness guarantees with the use of MUST. + + 88) Note that clients should read response data until the connection + is closed instead of immediately closing on a BYE. + + 89) Change _R_F_C_-_8_2_2 references to _R_F_C_-_2_8_2_2. + + 90) Clarify that _R_F_C_-_2_8_2_2 should be followed instead of _R_F_C_-_8_2_2. + + 91) Change recommendation of optional automatic capabilities in LOGIN + and AUTHENTICATE to use the CAPABILITY response code in the tagged + OK. This is more interoperable than an unsolicited untagged + CAPABILITY response. + + 92) STARTTLS and AUTH=PLAIN are mandatory to implement; add + recommendations for other [SASL] mechanisms. + + 93) Clarify that a "connection" (as opposed to "server" or "command") + is in one of the four states. + + 94) Clarify that a failed or rejected command does not change state. + + 95) Split references between normative and informative. + + 96) Discuss authentication failure issues in security section. + + 97) Clarify that a data item is not necessarily of only one data + type. + + 98) Clarify that sequence ranges are independent of order. + + 99) Change an example to clarify that superfluous shifts in + Modified-UTF7 can not be fixed just by omitting the shift. The + entire string must be recalculated. + + 100) Change Envelope Structure definition since [_R_F_C_-_2_8_2_2] uses + "envelope" to refer to the [SMTP] envelope and not the envelope data + that appears in the [_R_F_C_-_2_8_2_2] header. + + 101) Expand on _R_F_C_8_2_2.HEADER response data vs. BODY[HEADER]. + + 102) Clarify Logout state semantics, change ASCII art. + + 103) Security changes to comply with IESG requirements. + + 104) Add definition for body URI. + + 105) Break sequence range definition into three rules, with rewritten + descriptions for each. + + 106) Move STARTTLS and LOGINDISABLED here from [IMAP-TLS]. + + 107) Add IANA Considerations section. + + 108) Clarify valid client assumptions for new message UIDs vs. + UIDNEXT. + + 109) Clarify that changes to permanentflags affect concurrent + sessions as well as subsequent sessions. + + 110) Clarify that authenticated state can be entered by the CLOSE + command. + + 111) Emphasize that SELECT and EXAMINE are the exceptions to the rule + that a failing command does not change state. + + 112) Clarify that newly-appended messages have the Recent flag set. + + 113) Clarify that newly-copied messages SHOULD have the Recent flag + set. + + 114) Clarify that UID commands always return the UID in FETCH + responses. + +C. Key Word Index + + +FLAGS <flag list> (store command data item) ............... 59 + +FLAGS.SILENT <flag list> (store command data item) ........ 59 + -FLAGS <flag list> (store command data item) ............... 59 + -FLAGS.SILENT <flag list> (store command data item) ........ 59 + ALERT (response code) ...................................... 64 + ALL (fetch item) ........................................... 55 + ALL (search key) ........................................... 50 + ANSWERED (search key) ...................................... 50 + APPEND (command) ........................................... 45 + AUTHENTICATE (command) ..................................... 27 + BAD (response) ............................................. 66 + BADCHARSET (response code) ................................. 64 + BCC <string> (search key) .................................. 51 + BEFORE <date> (search key) ................................. 51 + BODY (fetch item) .......................................... 55 + BODY (fetch result) ........................................ 73 + BODY <string> (search key) ................................. 51 + + BODY.PEEK[<section>]<<partial>> (fetch item) ............... 57 + BODYSTRUCTURE (fetch item) ................................. 57 + BODYSTRUCTURE (fetch result) ............................... 74 + BODY[<section>]<<origin octet>> (fetch result) ............. 74 + BODY[<section>]<<partial>> (fetch item) .................... 55 + BYE (response) ............................................. 67 + Body Structure (message attribute) ......................... 12 + CAPABILITY (command) ....................................... 24 + CAPABILITY (response code) ................................. 64 + CAPABILITY (response) ...................................... 68 + CC <string> (search key) ................................... 51 + CHECK (command) ............................................ 47 + CLOSE (command) ............................................ 48 + COPY (command) ............................................. 59 + CREATE (command) ........................................... 34 + DELETE (command) ........................................... 35 + DELETED (search key) ....................................... 51 + DRAFT (search key) ......................................... 51 + ENVELOPE (fetch item) ...................................... 57 + ENVELOPE (fetch result) .................................... 77 + EXAMINE (command) .......................................... 33 + EXISTS (response) .......................................... 71 + EXPUNGE (command) .......................................... 48 + EXPUNGE (response) ......................................... 72 + Envelope Structure (message attribute) ..................... 12 + FAST (fetch item) .......................................... 55 + FETCH (command) ............................................ 54 + FETCH (response) ........................................... 73 + FLAGGED (search key) ....................................... 51 + FLAGS (fetch item) ......................................... 57 + FLAGS (fetch result) ....................................... 78 + FLAGS (response) ........................................... 71 + FLAGS <flag list> (store command data item) ................ 59 + FLAGS.SILENT <flag list> (store command data item) ......... 59 + FROM <string> (search key) ................................. 51 + FULL (fetch item) .......................................... 55 + Flags (message attribute) .................................. 11 + HEADER (part specifier) .................................... 55 + HEADER <field-name> <string> (search key) .................. 51 + HEADER.FIELDS <header-list> (part specifier) ............... 55 + HEADER.FIELDS.NOT <header-list> (part specifier) ........... 55 + INTERNALDATE (fetch item) .................................. 57 + INTERNALDATE (fetch result) ................................ 78 + Internal Date (message attribute) .......................... 12 + KEYWORD <flag> (search key) ................................ 51 + Keyword (type of flag) ..................................... 11 + LARGER <n> (search key) .................................... 51 + LIST (command) ............................................. 40 + + LIST (response) ............................................ 69 + LOGIN (command) ............................................ 30 + LOGOUT (command) ........................................... 25 + LSUB (command) ............................................. 43 + LSUB (response) ............................................ 70 + MAY (specification requirement term) ....................... 4 + MESSAGES (status item) ..................................... 45 + MIME (part specifier) ...................................... 56 + MUST (specification requirement term) ...................... 4 + MUST NOT (specification requirement term) .................. 4 + Message Sequence Number (message attribute) ................ 10 + NEW (search key) ........................................... 51 + NO (response) .............................................. 66 + NOOP (command) ............................................. 25 + NOT <search-key> (search key) .............................. 52 + OK (response) .............................................. 65 + OLD (search key) ........................................... 52 + ON <date> (search key) ..................................... 52 + OPTIONAL (specification requirement term) .................. 4 + OR <search-key1> <search-key2> (search key) ................ 52 + PARSE (response code) ...................................... 64 + PERMANENTFLAGS (response code) ............................. 64 + PREAUTH (response) ......................................... 67 + Permanent Flag (class of flag) ............................. 12 + READ-ONLY (response code) .................................. 65 + READ-WRITE (response code) ................................. 65 + RECENT (response) .......................................... 72 + RECENT (search key) ........................................ 52 + RECENT (status item) ....................................... 45 + RENAME (command) ........................................... 37 + REQUIRED (specification requirement term) .................. 4 + _R_F_C_8_2_2 (fetch item) ........................................ 57 + _R_F_C_8_2_2 (fetch result) ...................................... 78 + _R_F_C_8_2_2.HEADER (fetch item) ................................. 57 + _R_F_C_8_2_2.HEADER (fetch result) ............................... 78 + _R_F_C_8_2_2.SIZE (fetch item) ................................... 57 + _R_F_C_8_2_2.SIZE (fetch result) ................................. 78 + _R_F_C_8_2_2.TEXT (fetch item) ................................... 58 + _R_F_C_8_2_2.TEXT (fetch result) ................................. 79 + SEARCH (command) ........................................... 49 + SEARCH (response) .......................................... 71 + SEEN (search key) .......................................... 52 + SELECT (command) ........................................... 31 + SENTBEFORE <date> (search key) ............................. 52 + SENTON <date> (search key) ................................. 52 + SENTSINCE <date> (search key) .............................. 52 + SHOULD (specification requirement term) .................... 4 + SHOULD NOT (specification requirement term) ................ 4 + + SINCE <date> (search key) .................................. 52 + SMALLER <n> (search key) ................................... 52 + STARTTLS (command) ......................................... 27 + STATUS (command) ........................................... 44 + STATUS (response) .......................................... 70 + STORE (command) ............................................ 58 + SUBJECT <string> (search key) .............................. 53 + SUBSCRIBE (command) ........................................ 38 + Session Flag (class of flag) ............................... 12 + System Flag (type of flag) ................................. 11 + TEXT (part specifier) ...................................... 56 + TEXT <string> (search key) ................................. 53 + TO <string> (search key) ................................... 53 + TRYCREATE (response code) .................................. 65 + UID (command) .............................................. 60 + UID (fetch item) ........................................... 58 + UID (fetch result) ......................................... 79 + UID <sequence set> (search key) ............................ 53 + UIDNEXT (response code) .................................... 65 + UIDNEXT (status item) ...................................... 45 + UIDVALIDITY (response code) ................................ 65 + UIDVALIDITY (status item) .................................. 45 + UNANSWERED (search key) .................................... 53 + UNDELETED (search key) ..................................... 53 + UNDRAFT (search key) ....................................... 53 + UNFLAGGED (search key) ..................................... 53 + UNKEYWORD <flag> (search key) .............................. 53 + UNSEEN (response code) ..................................... 65 + UNSEEN (search key) ........................................ 53 + UNSEEN (status item) ....................................... 45 + UNSUBSCRIBE (command) ...................................... 39 + Unique Identifier (UID) (message attribute) ................ 8 + X<atom> (command) .......................................... 62 + [_R_F_C_-_2_8_2_2] Size (message attribute) ........................ 12 + \Answered (system flag) .................................... 11 + \Deleted (system flag) ..................................... 11 + \Draft (system flag) ....................................... 11 + \Flagged (system flag) ..................................... 11 + \Marked (mailbox name attribute) ........................... 69 + \Noinferiors (mailbox name attribute) ...................... 69 + \Noselect (mailbox name attribute) ......................... 69 + \Recent (system flag) ...................................... 11 + \Seen (system flag) ........................................ 11 + \Unmarked (mailbox name attribute) ......................... 69 + +Author's Address + + Mark R. Crispin + Networks and Distributed Computing + University of Washington + 4545 15th Avenue NE + Seattle, WA 98105-4527 + + Phone: (206) 543-5762 + + EMail: _M_R_C_@_C_A_C_._W_a_s_h_i_n_g_t_o_n_._E_D_U + +Full Copyright Statement + + Copyright (C) The Internet Society (2003). All Rights Reserved. + + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. v This + document and the information contained herein is provided on an "AS + IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK + FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT + LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL + NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY + OR FITNESS FOR A PARTICULAR PURPOSE. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + +Comments about this RFC: + * _R_F_C_ _3_5_0_1_:_ _T_h_o_u_g_h_t_s_ _a_n_d_ _s_u_g_g_e_s_t_i_o_n_s_:_A_b_i_l_i_t_y_ _t_o_ _p_r_o_v_i_d_e_ _m_u_l_t_i_p_l_e + _c_o_n_n_e_c_t_i_o_n_s_ _t_o_ _t_h_e_ _s_a_m_e_._._. by Chinmay (10/27/2003) + * _R_F_C_ _3_5_0_1_:_ _T_h_e_ _s_e_r_v_e_r_ _s_h_o_u_l_d_ _b_e_ _a_b_l_e_ _t_o_ _a_s_s_i_g_n_ _"_t_e_m_p_o_r_a_r_y_ _c_r_e_d_e_n_t_i_a_l_s_"_,_ _s_o + _t_h_a_t_ _a_ _u_s_e_r_._._. by Fredrik Tolf (7/15/2004) + * _R_F_C_ _3_5_0_1_:_ _U_N_S_E_E_N_ _v_a_l_u_e_ _w_i_t_h_ _S_t_a_t_u_s_ _C_o_m_m_a_n_d_ _a_n_d_ _U_N_S_E_E_N_ _f_l_a_g_s_ _s_h_o_u_l_d_ _w_i_t_h + _d_i_f_f_e_r_e_n_t_ _n_a_m_e_. by Ravi Prakash Gupta (12/28/2004) + +Previous: _R_F_C_ _3_4_9_9_ _-_ _R_e_q_u_e_s_t_ _f_o_r Next: _R_F_C_ _3_5_0_2_ _-_ _I_n_t_e_r_n_e_t_ _M_e_s_s_a_g_e +_C_o_m_m_e_n_t_s_ _S_u_m_m_a_r_y_ _R_F_C_ _N_u_m_b_e_r_s_ _3_4_0_0_-_3_4_9_9 _A_c_c_e_s_s_ _P_r_o_t_o_c_o_l_ _(_I_M_A_P_)_ _-_ _M_U_L_T_I_A_P_P_E_N_D + _E_x_t_e_n_s_i_o_n + +=============================================================================== + [ _R_F_C_ _I_n_d_e_x | _R_F_C_ _S_e_a_r_c_h | _U_s_e_n_e_t_ _F_A_Q_s | _W_e_b_ _F_A_Q_s | _D_o_c_u_m_e_n_t_s | _C_i_t_i_e_s ] + 2008 FAQS.ORG. All rights reserved. + diff --git a/doc/pop3-rfc1939.txt b/doc/pop3-rfc1939.txt @@ -0,0 +1,1291 @@ + + + + + + +Network Working Group J. Myers +Request for Comments: 1939 Carnegie Mellon +STD: 53 M. Rose +Obsoletes: 1725 Dover Beach Consulting, Inc. +Category: Standards Track May 1996 + + + Post Office Protocol - Version 3 + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Table of Contents + + 1. Introduction ................................................ 2 + 2. A Short Digression .......................................... 2 + 3. Basic Operation ............................................. 3 + 4. The AUTHORIZATION State ..................................... 4 + QUIT Command ................................................ 5 + 5. The TRANSACTION State ....................................... 5 + STAT Command ................................................ 6 + LIST Command ................................................ 6 + RETR Command ................................................ 8 + DELE Command ................................................ 8 + NOOP Command ................................................ 9 + RSET Command ................................................ 9 + 6. The UPDATE State ............................................ 10 + QUIT Command ................................................ 10 + 7. Optional POP3 Commands ...................................... 11 + TOP Command ................................................. 11 + UIDL Command ................................................ 12 + USER Command ................................................ 13 + PASS Command ................................................ 14 + APOP Command ................................................ 15 + 8. Scaling and Operational Considerations ...................... 16 + 9. POP3 Command Summary ........................................ 18 + 10. Example POP3 Session ....................................... 19 + 11. Message Format ............................................. 19 + 12. References ................................................. 20 + 13. Security Considerations .................................... 20 + 14. Acknowledgements ........................................... 20 + 15. Authors' Addresses ......................................... 21 + Appendix A. Differences from RFC 1725 .......................... 22 + + + +Myers & Rose Standards Track [Page 1] + +RFC 1939 POP3 May 1996 + + + Appendix B. Command Index ...................................... 23 + +1. Introduction + + On certain types of smaller nodes in the Internet it is often + impractical to maintain a message transport system (MTS). For + example, a workstation may not have sufficient resources (cycles, + disk space) in order to permit a SMTP server [RFC821] and associated + local mail delivery system to be kept resident and continuously + running. Similarly, it may be expensive (or impossible) to keep a + personal computer interconnected to an IP-style network for long + amounts of time (the node is lacking the resource known as + "connectivity"). + + Despite this, it is often very useful to be able to manage mail on + these smaller nodes, and they often support a user agent (UA) to aid + the tasks of mail handling. To solve this problem, a node which can + support an MTS entity offers a maildrop service to these less endowed + nodes. The Post Office Protocol - Version 3 (POP3) is intended to + permit a workstation to dynamically access a maildrop on a server + host in a useful fashion. Usually, this means that the POP3 protocol + is used to allow a workstation to retrieve mail that the server is + holding for it. + + POP3 is not intended to provide extensive manipulation operations of + mail on the server; normally, mail is downloaded and then deleted. A + more advanced (and complex) protocol, IMAP4, is discussed in + [RFC1730]. + + For the remainder of this memo, the term "client host" refers to a + host making use of the POP3 service, while the term "server host" + refers to a host which offers the POP3 service. + +2. A Short Digression + + This memo does not specify how a client host enters mail into the + transport system, although a method consistent with the philosophy of + this memo is presented here: + + When the user agent on a client host wishes to enter a message + into the transport system, it establishes an SMTP connection to + its relay host and sends all mail to it. This relay host could + be, but need not be, the POP3 server host for the client host. Of + course, the relay host must accept mail for delivery to arbitrary + recipient addresses, that functionality is not required of all + SMTP servers. + + + + + +Myers & Rose Standards Track [Page 2] + +RFC 1939 POP3 May 1996 + + +3. Basic Operation + + Initially, the server host starts the POP3 service by listening on + TCP port 110. When a client host wishes to make use of the service, + it establishes a TCP connection with the server host. When the + connection is established, the POP3 server sends a greeting. The + client and POP3 server then exchange commands and responses + (respectively) until the connection is closed or aborted. + + Commands in the POP3 consist of a case-insensitive keyword, possibly + followed by one or more arguments. All commands are terminated by a + CRLF pair. Keywords and arguments consist of printable ASCII + characters. Keywords and arguments are each separated by a single + SPACE character. Keywords are three or four characters long. Each + argument may be up to 40 characters long. + + Responses in the POP3 consist of a status indicator and a keyword + possibly followed by additional information. All responses are + terminated by a CRLF pair. Responses may be up to 512 characters + long, including the terminating CRLF. There are currently two status + indicators: positive ("+OK") and negative ("-ERR"). Servers MUST + send the "+OK" and "-ERR" in upper case. + + Responses to certain commands are multi-line. In these cases, which + are clearly indicated below, after sending the first line of the + response and a CRLF, any additional lines are sent, each terminated + by a CRLF pair. When all lines of the response have been sent, a + final line is sent, consisting of a termination octet (decimal code + 046, ".") and a CRLF pair. If any line of the multi-line response + begins with the termination octet, the line is "byte-stuffed" by + pre-pending the termination octet to that line of the response. + Hence a multi-line response is terminated with the five octets + "CRLF.CRLF". When examining a multi-line response, the client checks + to see if the line begins with the termination octet. If so and if + octets other than CRLF follow, the first octet of the line (the + termination octet) is stripped away. If so and if CRLF immediately + follows the termination character, then the response from the POP + server is ended and the line containing ".CRLF" is not considered + part of the multi-line response. + + A POP3 session progresses through a number of states during its + lifetime. Once the TCP connection has been opened and the POP3 + server has sent the greeting, the session enters the AUTHORIZATION + state. In this state, the client must identify itself to the POP3 + server. Once the client has successfully done this, the server + acquires resources associated with the client's maildrop, and the + session enters the TRANSACTION state. In this state, the client + requests actions on the part of the POP3 server. When the client has + + + +Myers & Rose Standards Track [Page 3] + +RFC 1939 POP3 May 1996 + + + issued the QUIT command, the session enters the UPDATE state. In + this state, the POP3 server releases any resources acquired during + the TRANSACTION state and says goodbye. The TCP connection is then + closed. + + A server MUST respond to an unrecognized, unimplemented, or + syntactically invalid command by responding with a negative status + indicator. A server MUST respond to a command issued when the + session is in an incorrect state by responding with a negative status + indicator. There is no general method for a client to distinguish + between a server which does not implement an optional command and a + server which is unwilling or unable to process the command. + + A POP3 server MAY have an inactivity autologout timer. Such a timer + MUST be of at least 10 minutes' duration. The receipt of any command + from the client during that interval should suffice to reset the + autologout timer. When the timer expires, the session does NOT enter + the UPDATE state--the server should close the TCP connection without + removing any messages or sending any response to the client. + +4. The AUTHORIZATION State + + Once the TCP connection has been opened by a POP3 client, the POP3 + server issues a one line greeting. This can be any positive + response. An example might be: + + S: +OK POP3 server ready + + The POP3 session is now in the AUTHORIZATION state. The client must + now identify and authenticate itself to the POP3 server. Two + possible mechanisms for doing this are described in this document, + the USER and PASS command combination and the APOP command. Both + mechanisms are described later in this document. Additional + authentication mechanisms are described in [RFC1734]. While there is + no single authentication mechanism that is required of all POP3 + servers, a POP3 server must of course support at least one + authentication mechanism. + + Once the POP3 server has determined through the use of any + authentication command that the client should be given access to the + appropriate maildrop, the POP3 server then acquires an exclusive- + access lock on the maildrop, as necessary to prevent messages from + being modified or removed before the session enters the UPDATE state. + If the lock is successfully acquired, the POP3 server responds with a + positive status indicator. The POP3 session now enters the + TRANSACTION state, with no messages marked as deleted. If the + maildrop cannot be opened for some reason (for example, a lock can + not be acquired, the client is denied access to the appropriate + + + +Myers & Rose Standards Track [Page 4] + +RFC 1939 POP3 May 1996 + + + maildrop, or the maildrop cannot be parsed), the POP3 server responds + with a negative status indicator. (If a lock was acquired but the + POP3 server intends to respond with a negative status indicator, the + POP3 server must release the lock prior to rejecting the command.) + After returning a negative status indicator, the server may close the + connection. If the server does not close the connection, the client + may either issue a new authentication command and start again, or the + client may issue the QUIT command. + + After the POP3 server has opened the maildrop, it assigns a message- + number to each message, and notes the size of each message in octets. + The first message in the maildrop is assigned a message-number of + "1", the second is assigned "2", and so on, so that the nth message + in a maildrop is assigned a message-number of "n". In POP3 commands + and responses, all message-numbers and message sizes are expressed in + base-10 (i.e., decimal). + + Here is the summary for the QUIT command when used in the + AUTHORIZATION state: + + QUIT + + Arguments: none + + Restrictions: none + + Possible Responses: + +OK + + Examples: + C: QUIT + S: +OK dewey POP3 server signing off + +5. The TRANSACTION State + + Once the client has successfully identified itself to the POP3 server + and the POP3 server has locked and opened the appropriate maildrop, + the POP3 session is now in the TRANSACTION state. The client may now + issue any of the following POP3 commands repeatedly. After each + command, the POP3 server issues a response. Eventually, the client + issues the QUIT command and the POP3 session enters the UPDATE state. + + + + + + + + + + +Myers & Rose Standards Track [Page 5] + +RFC 1939 POP3 May 1996 + + + Here are the POP3 commands valid in the TRANSACTION state: + + STAT + + Arguments: none + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + The POP3 server issues a positive response with a line + containing information for the maildrop. This line is + called a "drop listing" for that maildrop. + + In order to simplify parsing, all POP3 servers are + required to use a certain format for drop listings. The + positive response consists of "+OK" followed by a single + space, the number of messages in the maildrop, a single + space, and the size of the maildrop in octets. This memo + makes no requirement on what follows the maildrop size. + Minimal implementations should just end that line of the + response with a CRLF pair. More advanced implementations + may include other information. + + NOTE: This memo STRONGLY discourages implementations + from supplying additional information in the drop + listing. Other, optional, facilities are discussed + later on which permit the client to parse the messages + in the maildrop. + + Note that messages marked as deleted are not counted in + either total. + + Possible Responses: + +OK nn mm + + Examples: + C: STAT + S: +OK 2 320 + + + LIST [msg] + + Arguments: + a message-number (optional), which, if present, may NOT + refer to a message marked as deleted + + + + + +Myers & Rose Standards Track [Page 6] + +RFC 1939 POP3 May 1996 + + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + If an argument was given and the POP3 server issues a + positive response with a line containing information for + that message. This line is called a "scan listing" for + that message. + + If no argument was given and the POP3 server issues a + positive response, then the response given is multi-line. + After the initial +OK, for each message in the maildrop, + the POP3 server responds with a line containing + information for that message. This line is also called a + "scan listing" for that message. If there are no + messages in the maildrop, then the POP3 server responds + with no scan listings--it issues a positive response + followed by a line containing a termination octet and a + CRLF pair. + + In order to simplify parsing, all POP3 servers are + required to use a certain format for scan listings. A + scan listing consists of the message-number of the + message, followed by a single space and the exact size of + the message in octets. Methods for calculating the exact + size of the message are described in the "Message Format" + section below. This memo makes no requirement on what + follows the message size in the scan listing. Minimal + implementations should just end that line of the response + with a CRLF pair. More advanced implementations may + include other information, as parsed from the message. + + NOTE: This memo STRONGLY discourages implementations + from supplying additional information in the scan + listing. Other, optional, facilities are discussed + later on which permit the client to parse the messages + in the maildrop. + + Note that messages marked as deleted are not listed. + + Possible Responses: + +OK scan listing follows + -ERR no such message + + Examples: + C: LIST + S: +OK 2 messages (320 octets) + S: 1 120 + + + +Myers & Rose Standards Track [Page 7] + +RFC 1939 POP3 May 1996 + + + S: 2 200 + S: . + ... + C: LIST 2 + S: +OK 2 200 + ... + C: LIST 3 + S: -ERR no such message, only 2 messages in maildrop + + + RETR msg + + Arguments: + a message-number (required) which may NOT refer to a + message marked as deleted + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + If the POP3 server issues a positive response, then the + response given is multi-line. After the initial +OK, the + POP3 server sends the message corresponding to the given + message-number, being careful to byte-stuff the termination + character (as with all multi-line responses). + + Possible Responses: + +OK message follows + -ERR no such message + + Examples: + C: RETR 1 + S: +OK 120 octets + S: <the POP3 server sends the entire message here> + S: . + + + DELE msg + + Arguments: + a message-number (required) which may NOT refer to a + message marked as deleted + + Restrictions: + may only be given in the TRANSACTION state + + + + + + +Myers & Rose Standards Track [Page 8] + +RFC 1939 POP3 May 1996 + + + Discussion: + The POP3 server marks the message as deleted. Any future + reference to the message-number associated with the message + in a POP3 command generates an error. The POP3 server does + not actually delete the message until the POP3 session + enters the UPDATE state. + + Possible Responses: + +OK message deleted + -ERR no such message + + Examples: + C: DELE 1 + S: +OK message 1 deleted + ... + C: DELE 2 + S: -ERR message 2 already deleted + + + NOOP + + Arguments: none + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + The POP3 server does nothing, it merely replies with a + positive response. + + Possible Responses: + +OK + + Examples: + C: NOOP + S: +OK + + + RSET + + Arguments: none + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + If any messages have been marked as deleted by the POP3 + server, they are unmarked. The POP3 server then replies + + + +Myers & Rose Standards Track [Page 9] + +RFC 1939 POP3 May 1996 + + + with a positive response. + + Possible Responses: + +OK + + Examples: + C: RSET + S: +OK maildrop has 2 messages (320 octets) + +6. The UPDATE State + + When the client issues the QUIT command from the TRANSACTION state, + the POP3 session enters the UPDATE state. (Note that if the client + issues the QUIT command from the AUTHORIZATION state, the POP3 + session terminates but does NOT enter the UPDATE state.) + + If a session terminates for some reason other than a client-issued + QUIT command, the POP3 session does NOT enter the UPDATE state and + MUST not remove any messages from the maildrop. + + QUIT + + Arguments: none + + Restrictions: none + + Discussion: + The POP3 server removes all messages marked as deleted + from the maildrop and replies as to the status of this + operation. If there is an error, such as a resource + shortage, encountered while removing messages, the + maildrop may result in having some or none of the messages + marked as deleted be removed. In no case may the server + remove any messages not marked as deleted. + + Whether the removal was successful or not, the server + then releases any exclusive-access lock on the maildrop + and closes the TCP connection. + + Possible Responses: + +OK + -ERR some deleted messages not removed + + Examples: + C: QUIT + S: +OK dewey POP3 server signing off (maildrop empty) + ... + C: QUIT + + + +Myers & Rose Standards Track [Page 10] + +RFC 1939 POP3 May 1996 + + + S: +OK dewey POP3 server signing off (2 messages left) + ... + +7. Optional POP3 Commands + + The POP3 commands discussed above must be supported by all minimal + implementations of POP3 servers. + + The optional POP3 commands described below permit a POP3 client + greater freedom in message handling, while preserving a simple POP3 + server implementation. + + NOTE: This memo STRONGLY encourages implementations to support + these commands in lieu of developing augmented drop and scan + listings. In short, the philosophy of this memo is to put + intelligence in the part of the POP3 client and not the POP3 + server. + + TOP msg n + + Arguments: + a message-number (required) which may NOT refer to to a + message marked as deleted, and a non-negative number + of lines (required) + + Restrictions: + may only be given in the TRANSACTION state + + Discussion: + If the POP3 server issues a positive response, then the + response given is multi-line. After the initial +OK, the + POP3 server sends the headers of the message, the blank + line separating the headers from the body, and then the + number of lines of the indicated message's body, being + careful to byte-stuff the termination character (as with + all multi-line responses). + + Note that if the number of lines requested by the POP3 + client is greater than than the number of lines in the + body, then the POP3 server sends the entire message. + + Possible Responses: + +OK top of message follows + -ERR no such message + + Examples: + C: TOP 1 10 + S: +OK + + + +Myers & Rose Standards Track [Page 11] + +RFC 1939 POP3 May 1996 + + + S: <the POP3 server sends the headers of the + message, a blank line, and the first 10 lines + of the body of the message> + S: . + ... + C: TOP 100 3 + S: -ERR no such message + + + UIDL [msg] + + Arguments: + a message-number (optional), which, if present, may NOT + refer to a message marked as deleted + + Restrictions: + may only be given in the TRANSACTION state. + + Discussion: + If an argument was given and the POP3 server issues a positive + response with a line containing information for that message. + This line is called a "unique-id listing" for that message. + + If no argument was given and the POP3 server issues a positive + response, then the response given is multi-line. After the + initial +OK, for each message in the maildrop, the POP3 server + responds with a line containing information for that message. + This line is called a "unique-id listing" for that message. + + In order to simplify parsing, all POP3 servers are required to + use a certain format for unique-id listings. A unique-id + listing consists of the message-number of the message, + followed by a single space and the unique-id of the message. + No information follows the unique-id in the unique-id listing. + + The unique-id of a message is an arbitrary server-determined + string, consisting of one to 70 characters in the range 0x21 + to 0x7E, which uniquely identifies a message within a + maildrop and which persists across sessions. This + persistence is required even if a session ends without + entering the UPDATE state. The server should never reuse an + unique-id in a given maildrop, for as long as the entity + using the unique-id exists. + + Note that messages marked as deleted are not listed. + + While it is generally preferable for server implementations + to store arbitrarily assigned unique-ids in the maildrop, + + + +Myers & Rose Standards Track [Page 12] + +RFC 1939 POP3 May 1996 + + + this specification is intended to permit unique-ids to be + calculated as a hash of the message. Clients should be able + to handle a situation where two identical copies of a + message in a maildrop have the same unique-id. + + Possible Responses: + +OK unique-id listing follows + -ERR no such message + + Examples: + C: UIDL + S: +OK + S: 1 whqtswO00WBw418f9t5JxYwZ + S: 2 QhdPYR:00WBw1Ph7x7 + S: . + ... + C: UIDL 2 + S: +OK 2 QhdPYR:00WBw1Ph7x7 + ... + C: UIDL 3 + S: -ERR no such message, only 2 messages in maildrop + + + USER name + + Arguments: + a string identifying a mailbox (required), which is of + significance ONLY to the server + + Restrictions: + may only be given in the AUTHORIZATION state after the POP3 + greeting or after an unsuccessful USER or PASS command + + Discussion: + To authenticate using the USER and PASS command + combination, the client must first issue the USER + command. If the POP3 server responds with a positive + status indicator ("+OK"), then the client may issue + either the PASS command to complete the authentication, + or the QUIT command to terminate the POP3 session. If + the POP3 server responds with a negative status indicator + ("-ERR") to the USER command, then the client may either + issue a new authentication command or may issue the QUIT + command. + + The server may return a positive response even though no + such mailbox exists. The server may return a negative + response if mailbox exists, but does not permit plaintext + + + +Myers & Rose Standards Track [Page 13] + +RFC 1939 POP3 May 1996 + + + password authentication. + + Possible Responses: + +OK name is a valid mailbox + -ERR never heard of mailbox name + + Examples: + C: USER frated + S: -ERR sorry, no mailbox for frated here + ... + C: USER mrose + S: +OK mrose is a real hoopy frood + + + PASS string + + Arguments: + a server/mailbox-specific password (required) + + Restrictions: + may only be given in the AUTHORIZATION state immediately + after a successful USER command + + Discussion: + When the client issues the PASS command, the POP3 server + uses the argument pair from the USER and PASS commands to + determine if the client should be given access to the + appropriate maildrop. + + Since the PASS command has exactly one argument, a POP3 + server may treat spaces in the argument as part of the + password, instead of as argument separators. + + Possible Responses: + +OK maildrop locked and ready + -ERR invalid password + -ERR unable to lock maildrop + + Examples: + C: USER mrose + S: +OK mrose is a real hoopy frood + C: PASS secret + S: -ERR maildrop already locked + ... + C: USER mrose + S: +OK mrose is a real hoopy frood + C: PASS secret + S: +OK mrose's maildrop has 2 messages (320 octets) + + + +Myers & Rose Standards Track [Page 14] + +RFC 1939 POP3 May 1996 + + + APOP name digest + + Arguments: + a string identifying a mailbox and a MD5 digest string + (both required) + + Restrictions: + may only be given in the AUTHORIZATION state after the POP3 + greeting or after an unsuccessful USER or PASS command + + Discussion: + Normally, each POP3 session starts with a USER/PASS + exchange. This results in a server/user-id specific + password being sent in the clear on the network. For + intermittent use of POP3, this may not introduce a sizable + risk. However, many POP3 client implementations connect to + the POP3 server on a regular basis -- to check for new + mail. Further the interval of session initiation may be on + the order of five minutes. Hence, the risk of password + capture is greatly enhanced. + + An alternate method of authentication is required which + provides for both origin authentication and replay + protection, but which does not involve sending a password + in the clear over the network. The APOP command provides + this functionality. + + A POP3 server which implements the APOP command will + include a timestamp in its banner greeting. The syntax of + the timestamp corresponds to the `msg-id' in [RFC822], and + MUST be different each time the POP3 server issues a banner + greeting. For example, on a UNIX implementation in which a + separate UNIX process is used for each instance of a POP3 + server, the syntax of the timestamp might be: + + <process-ID.clock@hostname> + + where `process-ID' is the decimal value of the process's + PID, clock is the decimal value of the system clock, and + hostname is the fully-qualified domain-name corresponding + to the host where the POP3 server is running. + + The POP3 client makes note of this timestamp, and then + issues the APOP command. The `name' parameter has + identical semantics to the `name' parameter of the USER + command. The `digest' parameter is calculated by applying + the MD5 algorithm [RFC1321] to a string consisting of the + timestamp (including angle-brackets) followed by a shared + + + +Myers & Rose Standards Track [Page 15] + +RFC 1939 POP3 May 1996 + + + secret. This shared secret is a string known only to the + POP3 client and server. Great care should be taken to + prevent unauthorized disclosure of the secret, as knowledge + of the secret will allow any entity to successfully + masquerade as the named user. The `digest' parameter + itself is a 16-octet value which is sent in hexadecimal + format, using lower-case ASCII characters. + + When the POP3 server receives the APOP command, it verifies + the digest provided. If the digest is correct, the POP3 + server issues a positive response, and the POP3 session + enters the TRANSACTION state. Otherwise, a negative + response is issued and the POP3 session remains in the + AUTHORIZATION state. + + Note that as the length of the shared secret increases, so + does the difficulty of deriving it. As such, shared + secrets should be long strings (considerably longer than + the 8-character example shown below). + + Possible Responses: + +OK maildrop locked and ready + -ERR permission denied + + Examples: + S: +OK POP3 server ready <1896.697170952@dbc.mtview.ca.us> + C: APOP mrose c4c9334bac560ecc979e58001b3e22fb + S: +OK maildrop has 1 message (369 octets) + + In this example, the shared secret is the string `tan- + staaf'. Hence, the MD5 algorithm is applied to the string + + <1896.697170952@dbc.mtview.ca.us>tanstaaf + + which produces a digest value of + + c4c9334bac560ecc979e58001b3e22fb + +8. Scaling and Operational Considerations + + Since some of the optional features described above were added to the + POP3 protocol, experience has accumulated in using them in large- + scale commercial post office operations where most of the users are + unrelated to each other. In these situations and others, users and + vendors of POP3 clients have discovered that the combination of using + the UIDL command and not issuing the DELE command can provide a weak + version of the "maildrop as semi-permanent repository" functionality + normally associated with IMAP. Of course the other capabilities of + + + +Myers & Rose Standards Track [Page 16] + +RFC 1939 POP3 May 1996 + + + IMAP, such as polling an existing connection for newly arrived + messages and supporting multiple folders on the server, are not + present in POP3. + + When these facilities are used in this way by casual users, there has + been a tendency for already-read messages to accumulate on the server + without bound. This is clearly an undesirable behavior pattern from + the standpoint of the server operator. This situation is aggravated + by the fact that the limited capabilities of the POP3 do not permit + efficient handling of maildrops which have hundreds or thousands of + messages. + + Consequently, it is recommended that operators of large-scale multi- + user servers, especially ones in which the user's only access to the + maildrop is via POP3, consider such options as: + + * Imposing a per-user maildrop storage quota or the like. + + A disadvantage to this option is that accumulation of messages may + result in the user's inability to receive new ones into the + maildrop. Sites which choose this option should be sure to inform + users of impending or current exhaustion of quota, perhaps by + inserting an appropriate message into the user's maildrop. + + * Enforce a site policy regarding mail retention on the server. + + Sites are free to establish local policy regarding the storage and + retention of messages on the server, both read and unread. For + example, a site might delete unread messages from the server after + 60 days and delete read messages after 7 days. Such message + deletions are outside the scope of the POP3 protocol and are not + considered a protocol violation. + + Server operators enforcing message deletion policies should take + care to make all users aware of the policies in force. + + Clients must not assume that a site policy will automate message + deletions, and should continue to explicitly delete messages using + the DELE command when appropriate. + + It should be noted that enforcing site message deletion policies + may be confusing to the user community, since their POP3 client + may contain configuration options to leave mail on the server + which will not in fact be supported by the server. + + One special case of a site policy is that messages may only be + downloaded once from the server, and are deleted after this has + been accomplished. This could be implemented in POP3 server + + + +Myers & Rose Standards Track [Page 17] + +RFC 1939 POP3 May 1996 + + + software by the following mechanism: "following a POP3 login by a + client which was ended by a QUIT, delete all messages downloaded + during the session with the RETR command". It is important not to + delete messages in the event of abnormal connection termination + (ie, if no QUIT was received from the client) because the client + may not have successfully received or stored the messages. + Servers implementing a download-and-delete policy may also wish to + disable or limit the optional TOP command, since it could be used + as an alternate mechanism to download entire messages. + +9. POP3 Command Summary + + Minimal POP3 Commands: + + USER name valid in the AUTHORIZATION state + PASS string + QUIT + + STAT valid in the TRANSACTION state + LIST [msg] + RETR msg + DELE msg + NOOP + RSET + QUIT + + Optional POP3 Commands: + + APOP name digest valid in the AUTHORIZATION state + + TOP msg n valid in the TRANSACTION state + UIDL [msg] + + POP3 Replies: + + +OK + -ERR + + Note that with the exception of the STAT, LIST, and UIDL commands, + the reply given by the POP3 server to any command is significant + only to "+OK" and "-ERR". Any text occurring after this reply + may be ignored by the client. + + + + + + + + + +Myers & Rose Standards Track [Page 18] + +RFC 1939 POP3 May 1996 + + +10. Example POP3 Session + + S: <wait for connection on TCP port 110> + C: <open connection> + S: +OK POP3 server ready <1896.697170952@dbc.mtview.ca.us> + C: APOP mrose c4c9334bac560ecc979e58001b3e22fb + S: +OK mrose's maildrop has 2 messages (320 octets) + C: STAT + S: +OK 2 320 + C: LIST + S: +OK 2 messages (320 octets) + S: 1 120 + S: 2 200 + S: . + C: RETR 1 + S: +OK 120 octets + S: <the POP3 server sends message 1> + S: . + C: DELE 1 + S: +OK message 1 deleted + C: RETR 2 + S: +OK 200 octets + S: <the POP3 server sends message 2> + S: . + C: DELE 2 + S: +OK message 2 deleted + C: QUIT + S: +OK dewey POP3 server signing off (maildrop empty) + C: <close connection> + S: <wait for next connection> + +11. Message Format + + All messages transmitted during a POP3 session are assumed to conform + to the standard for the format of Internet text messages [RFC822]. + + It is important to note that the octet count for a message on the + server host may differ from the octet count assigned to that message + due to local conventions for designating end-of-line. Usually, + during the AUTHORIZATION state of the POP3 session, the POP3 server + can calculate the size of each message in octets when it opens the + maildrop. For example, if the POP3 server host internally represents + end-of-line as a single character, then the POP3 server simply counts + each occurrence of this character in a message as two octets. Note + that lines in the message which start with the termination octet need + not (and must not) be counted twice, since the POP3 client will + remove all byte-stuffed termination characters when it receives a + multi-line response. + + + +Myers & Rose Standards Track [Page 19] + +RFC 1939 POP3 May 1996 + + +12. References + + [RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC + 821, USC/Information Sciences Institute, August 1982. + + [RFC822] Crocker, D., "Standard for the Format of ARPA-Internet Text + Messages", STD 11, RFC 822, University of Delaware, August 1982. + + [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, + MIT Laboratory for Computer Science, April 1992. + + [RFC1730] Crispin, M., "Internet Message Access Protocol - Version + 4", RFC 1730, University of Washington, December 1994. + + [RFC1734] Myers, J., "POP3 AUTHentication command", RFC 1734, + Carnegie Mellon, December 1994. + +13. Security Considerations + + It is conjectured that use of the APOP command provides origin + identification and replay protection for a POP3 session. + Accordingly, a POP3 server which implements both the PASS and APOP + commands should not allow both methods of access for a given user; + that is, for a given mailbox name, either the USER/PASS command + sequence or the APOP command is allowed, but not both. + + Further, note that as the length of the shared secret increases, so + does the difficulty of deriving it. + + Servers that answer -ERR to the USER command are giving potential + attackers clues about which names are valid. + + Use of the PASS command sends passwords in the clear over the + network. + + Use of the RETR and TOP commands sends mail in the clear over the + network. + + Otherwise, security issues are not discussed in this memo. + +14. Acknowledgements + + The POP family has a long and checkered history. Although primarily + a minor revision to RFC 1460, POP3 is based on the ideas presented in + RFCs 918, 937, and 1081. + + In addition, Alfred Grimstad, Keith McCloghrie, and Neil Ostroff + provided significant comments on the APOP command. + + + +Myers & Rose Standards Track [Page 20] + +RFC 1939 POP3 May 1996 + + +15. Authors' Addresses + + John G. Myers + Carnegie-Mellon University + 5000 Forbes Ave + Pittsburgh, PA 15213 + + EMail: jgm+@cmu.edu + + + Marshall T. Rose + Dover Beach Consulting, Inc. + 420 Whisman Court + Mountain View, CA 94043-2186 + + EMail: mrose@dbc.mtview.ca.us + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Rose Standards Track [Page 21] + +RFC 1939 POP3 May 1996 + + +Appendix A. Differences from RFC 1725 + + This memo is a revision to RFC 1725, a Draft Standard. It makes the + following changes from that document: + + - clarifies that command keywords are case insensitive. + + - specifies that servers must send "+OK" and "-ERR" in + upper case. + + - specifies that the initial greeting is a positive response, + instead of any string which should be a positive response. + + - clarifies behavior for unimplemented commands. + + - makes the USER and PASS commands optional. + + - clarified the set of possible responses to the USER command. + + - reverses the order of the examples in the USER and PASS + commands, to reduce confusion. + + - clarifies that the PASS command may only be given immediately + after a successful USER command. + + - clarified the persistence requirements of UIDs and added some + implementation notes. + + - specifies a UID length limitation of one to 70 octets. + + - specifies a status indicator length limitation + of 512 octets, including the CRLF. + + - clarifies that LIST with no arguments on an empty mailbox + returns success. + + - adds a reference from the LIST command to the Message Format + section + + - clarifies the behavior of QUIT upon failure + + - clarifies the security section to not imply the use of the + USER command with the APOP command. + + - adds references to RFCs 1730 and 1734 + + - clarifies the method by which a UA may enter mail into the + transport system. + + + +Myers & Rose Standards Track [Page 22] + +RFC 1939 POP3 May 1996 + + + - clarifies that the second argument to the TOP command is a + number of lines. + + - changes the suggestion in the Security Considerations section + for a server to not accept both PASS and APOP for a given user + from a "must" to a "should". + + - adds a section on scaling and operational considerations + +Appendix B. Command Index + + APOP ....................................................... 15 + DELE ....................................................... 8 + LIST ....................................................... 6 + NOOP ....................................................... 9 + PASS ....................................................... 14 + QUIT ....................................................... 5 + QUIT ....................................................... 10 + RETR ....................................................... 8 + RSET ....................................................... 9 + STAT ....................................................... 6 + TOP ........................................................ 11 + UIDL ....................................................... 12 + USER ....................................................... 13 + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Rose Standards Track [Page 23] + diff --git a/doc/smtp-rfc821.txt b/doc/smtp-rfc821.txt @@ -0,0 +1,2707 @@ + + SIMPLE MAIL TRANSFER PROTOCOL + + Jonathan B. Postel + + August 1982 + + Information Sciences Institute + University of Southern California + 4676 Admiralty Way + Marina del Rey, California 90291 + + (213) 822-1511 + + August 1982 + Simple Mail Transfer Protocol + + TABLE OF CONTENTS + + 1. INTRODUCTION .................................................. 1 + + 2. THE SMTP MODEL ................................................ 2 + + 3. THE SMTP PROCEDURE ............................................ 4 + + 3.1. Mail ..................................................... 4 + 3.2. Forwarding ............................................... 7 + 3.3. Verifying and Expanding .................................. 8 + 3.4. Sending and Mailing ..................................... 11 + 3.5. Opening and Closing ..................................... 13 + 3.6. Relaying ................................................ 14 + 3.7. Domains ................................................. 17 + 3.8. Changing Roles .......................................... 18 + + 4. THE SMTP SPECIFICATIONS ...................................... 19 + + 4.1. SMTP Commands ........................................... 19 + 4.1.1. Command Semantics ..................................... 19 + 4.1.2. Command Syntax ........................................ 27 + 4.2. SMTP Replies ............................................ 34 + 4.2.1. Reply Codes by Function Group ......................... 35 + 4.2.2. Reply Codes in Numeric Order .......................... 36 + 4.3. Sequencing of Commands and Replies ...................... 37 + 4.4. State Diagrams .......................................... 39 + 4.5. Details ................................................. 41 + 4.5.1. Minimum Implementation ................................ 41 + 4.5.2. Transparency .......................................... 41 + 4.5.3. Sizes ................................................. 42 + + APPENDIX A: TCP ................................................. 44 + APPENDIX B: NCP ................................................. 45 + APPENDIX C: NITS ................................................ 46 + APPENDIX D: X.25 ................................................ 47 + APPENDIX E: Theory of Reply Codes ............................... 48 + APPENDIX F: Scenarios ........................................... 51 + + GLOSSARY ......................................................... 64 + + REFERENCES ....................................................... 67 + +Network Working Group J. Postel +Request for Comments: DRAFT ISI +Replaces: _R_F_C_ _7_8_8, 780, 772 August 1982 + + SIMPLE MAIL TRANSFER PROTOCOL + +1. INTRODUCTION + + The objective of Simple Mail Transfer Protocol (SMTP) is to transfer + mail reliably and efficiently. + + SMTP is independent of the particular transmission subsystem and + requires only a reliable ordered data stream channel. Appendices A, + B, C, and D describe the use of SMTP with various transport services. + A Glossary provides the definitions of terms as used in this + document. + + An important feature of SMTP is its capability to relay mail across + transport service environments. A transport service provides an + interprocess communication environment (IPCE). An IPCE may cover one + network, several networks, or a subset of a network. It is important + to realize that transport systems (or IPCEs) are not one-to-one with + networks. A process can communicate directly with another process + through any mutually known IPCE. Mail is an application or use of + interprocess communication. Mail can be communicated between + processes in different IPCEs by relaying through a process connected + to two (or more) IPCEs. More specifically, mail can be relayed + between hosts on different transport systems by a host on both + transport systems. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +2. THE SMTP MODEL + + The SMTP design is based on the following model of communication: as + the result of a user mail request, the sender-SMTP establishes a + two-way transmission channel to a receiver-SMTP. The receiver-SMTP + may be either the ultimate destination or an intermediate. SMTP + commands are generated by the sender-SMTP and sent to the + receiver-SMTP. SMTP replies are sent from the receiver-SMTP to the + sender-SMTP in response to the commands. + + Once the transmission channel is established, the SMTP-sender sends a + MAIL command indicating the sender of the mail. If the SMTP-receiver + can accept mail it responds with an OK reply. The SMTP-sender then + sends a RCPT command identifying a recipient of the mail. If the + SMTP-receiver can accept mail for that recipient it responds with an + OK reply; if not, it responds with a reply rejecting that recipient + (but not the whole mail transaction). The SMTP-sender and + SMTP-receiver may negotiate several recipients. When the recipients + have been negotiated the SMTP-sender sends the mail data, terminating + with a special sequence. If the SMTP-receiver successfully processes + the mail data it responds with an OK reply. The dialog is purposely + lock-step, one-at-a-time. + + ------------------------------------------------------------- + + +----------+ +----------+ + +------+ | | | | + | User |<-->| | SMTP | | + +------+ | Sender- |Commands/Replies| Receiver-| + +------+ | SMTP |<-------------->| SMTP | +------+ + | File |<-->| | and Mail | |<-->| File | + |System| | | | | |System| + +------+ +----------+ +----------+ +------+ + + Sender-SMTP Receiver-SMTP + + Model for SMTP Use + + Figure 1 + + ------------------------------------------------------------- + + The SMTP provides mechanisms for the transmission of mail; directly + from the sending user's host to the receiving user's host when the + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + two host are connected to the same transport service, or via one or + more relay SMTP-servers when the source and destination hosts are not + connected to the same transport service. + + To be able to provide the relay capability the SMTP-server must be + supplied with the name of the ultimate destination host as well as + the destination mailbox name. + + The argument to the MAIL command is a reverse-path, which specifies + who the mail is from. The argument to the RCPT command is a + forward-path, which specifies who the mail is to. The forward-path + is a source route, while the reverse-path is a return route (which + may be used to return a message to the sender when an error occurs + with a relayed message). + + When the same message is sent to multiple recipients the SMTP + encourages the transmission of only one copy of the data for all the + recipients at the same destination host. + + The mail commands and replies have a rigid syntax. Replies also have + a numeric code. In the following, examples appear which use actual + commands and replies. The complete lists of commands and replies + appears in Section 4 on specifications. + + Commands and replies are not case sensitive. That is, a command or + reply word may be upper case, lower case, or any mixture of upper and + lower case. Note that this is not true of mailbox user names. For + some hosts the user name is case sensitive, and SMTP implementations + must take case to preserve the case of user names as they appear in + mailbox arguments. Host names are not case sensitive. + + Commands and replies are composed of characters from the ASCII + character set [1]. When the transport service provides an 8-bit byte + (octet) transmission channel, each 7-bit character is transmitted + right justified in an octet with the high order bit cleared to zero. + + When specifying the general form of a command or reply, an argument + (or special symbol) will be denoted by a meta-linguistic variable (or + constant), for example, "<string>" or "<reverse-path>". Here the + angle brackets indicate these are meta-linguistic variables. + However, some arguments use the angle brackets literally. For + example, an actual reverse-path is enclosed in angle brackets, i.e., + "<_J_o_h_n_._S_m_i_t_h_@_U_S_C_-_I_S_I_._A_R_P_A>" is an instance of <reverse-path> (the + angle brackets are actually transmitted in the command or reply). + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +3. THE SMTP PROCEDURES + + This section presents the procedures used in SMTP in several parts. + First comes the basic mail procedure defined as a mail transaction. + Following this are descriptions of forwarding mail, verifying mailbox + names and expanding mailing lists, sending to terminals instead of or + in combination with mailboxes, and the opening and closing exchanges. + At the end of this section are comments on relaying, a note on mail + domains, and a discussion of changing roles. Throughout this section + are examples of partial command and reply sequences, several complete + scenarios are presented in Appendix F. + + 3.1. MAIL + + There are three steps to SMTP mail transactions. The transaction + is started with a MAIL command which gives the sender + identification. A series of one or more RCPT commands follows + giving the receiver information. Then a DATA command gives the + mail data. And finally, the end of mail data indicator confirms + the transaction. + + The first step in the procedure is the MAIL command. The + <reverse-path> contains the source mailbox. + + MAIL <SP> FROM:<reverse-path> <CRLF> + + This command tells the SMTP-receiver that a new mail + transaction is starting and to reset all its state tables and + buffers, including any recipients or mail data. It gives the + reverse-path which can be used to report errors. If accepted, + the receiver-SMTP returns a 250 OK reply. + + The <reverse-path> can contain more than just a mailbox. The + <reverse-path> is a reverse source routing list of hosts and + source mailbox. The first host in the <reverse-path> should be + the host sending this command. + + The second step in the procedure is the RCPT command. + + RCPT <SP> TO:<forward-path> <CRLF> + + This command gives a forward-path identifying one recipient. + If accepted, the receiver-SMTP returns a 250 OK reply, and + stores the forward-path. If the recipient is unknown the + receiver-SMTP returns a 550 Failure reply. This second step of + the procedure can be repeated any number of times. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + The <forward-path> can contain more than just a mailbox. The + <forward-path> is a source routing list of hosts and the + destination mailbox. The first host in the <forward-path> + should be the host receiving this command. + + The third step in the procedure is the DATA command. + + DATA <CRLF> + + If accepted, the receiver-SMTP returns a 354 Intermediate reply + and considers all succeeding lines to be the message text. + When the end of text is received and stored the SMTP-receiver + sends a 250 OK reply. + + Since the mail data is sent on the transmission channel the end + of the mail data must be indicated so that the command and + reply dialog can be resumed. SMTP indicates the end of the + mail data by sending a line containing only a period. A + transparency procedure is used to prevent this from interfering + with the user's text (see Section 4.5.2). + + Please note that the mail data includes the memo header + items such as Date, Subject, To, Cc, From [2]. + + The end of mail data indicator also confirms the mail + transaction and tells the receiver-SMTP to now process the + stored recipients and mail data. If accepted, the + receiver-SMTP returns a 250 OK reply. The DATA command should + fail only if the mail transaction was incomplete (for example, + no recipients), or if resources are not available. + + The above procedure is an example of a mail transaction. These + commands must be used only in the order discussed above. + Example 1 (below) illustrates the use of these commands in a mail + transaction. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + ------------------------------------------------------------- + + Example of the SMTP Procedure + + This SMTP example shows mail sent by Smith at host Alpha.ARPA, + to Jones, Green, and Brown at host Beta.ARPA. Here we assume + that host Alpha contacts host Beta directly. + + S: MAIL FROM:<_S_m_i_t_h_@_A_l_p_h_a_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_J_o_n_e_s_@_B_e_t_a_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_G_r_e_e_n_@_B_e_t_a_._A_R_P_A> + R: 550 No such user here + + S: RCPT TO:<_B_r_o_w_n_@_B_e_t_a_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: <CRLF>.<CRLF> + R: 250 OK + + The mail has now been accepted for Jones and Brown. Green did + not have a mailbox at host Beta. + + Example 1 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 3.2. FORWARDING + + There are some cases where the destination information in the + <forward-path> is incorrect, but the receiver-SMTP knows the + correct destination. In such cases, one of the following replies + should be used to allow the sender to contact the correct + destination. + + 251 User not local; will forward to <forward-path> + + This reply indicates that the receiver-SMTP knows the user's + mailbox is on another host and indicates the correct + forward-path to use in the future. Note that either the + host or user or both may be different. The receiver takes + responsibility for delivering the message. + + 551 User not local; please try <forward-path> + + This reply indicates that the receiver-SMTP knows the user's + mailbox is on another host and indicates the correct + forward-path to use. Note that either the host or user or + both may be different. The receiver refuses to accept mail + for this user, and the sender must either redirect the mail + according to the information provided or return an error + response to the originating user. + + Example 2 illustrates the use of these responses. + + ------------------------------------------------------------- + + Example of Forwarding + + Either + + S: RCPT TO:<_P_o_s_t_e_l_@_U_S_C_-_I_S_I_._A_R_P_A> + R: 251 User not local; will forward to <_P_o_s_t_e_l_@_U_S_C_-_I_S_I_F_._A_R_P_A> + + Or + + S: RCPT TO:<_P_a_u_l_@_U_S_C_-_I_S_I_B_._A_R_P_A> + R: 551 User not local; please try <_M_o_c_k_a_p_e_t_r_i_s_@_U_S_C_-_I_S_I_F_._A_R_P_A> + + Example 2 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + 3.3. VERIFYING AND EXPANDING + + SMTP provides as additional features, commands to verify a user + name or expand a mailing list. This is done with the VRFY and + EXPN commands, which have character string arguments. For the + VRFY command, the string is a user name, and the response may + include the full name of the user and must include the mailbox of + the user. For the EXPN command, the string identifies a mailing + list, and the multiline response may include the full name of the + users and must give the mailboxes on the mailing list. + + "User name" is a fuzzy term and used purposely. If a host + implements the VRFY or EXPN commands then at least local mailboxes + must be recognized as "user names". If a host chooses to + recognize other strings as "user names" that is allowed. + + In some hosts the distinction between a mailing list and an alias + for a single mailbox is a bit fuzzy, since a common data structure + may hold both types of entries, and it is possible to have mailing + lists of one mailbox. If a request is made to verify a mailing + list a positive response can be given if on receipt of a message + so addressed it will be delivered to everyone on the list, + otherwise an error should be reported (e.g., "550 That is a + mailing list, not a user"). If a request is made to expand a user + name a positive response can be formed by returning a list + containing one name, or an error can be reported (e.g., "550 That + is a user name, not a mailing list"). + + In the case of a multiline reply (normal for EXPN) exactly one + mailbox is to be specified on each line of the reply. In the case + of an ambiguous request, for example, "VRFY Smith", where there + are two Smith's the response must be "553 User ambiguous". + + The case of verifying a user name is straightforward as shown in + example 3. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + ------------------------------------------------------------- + + Example of Verifying a User Name + + Either + + S: VRFY Smith + R: 250 Fred Smith <_S_m_i_t_h_@_U_S_C_-_I_S_I_F_._A_R_P_A> + + Or + + S: VRFY Smith + R: 251 User not local; will forward to <_S_m_i_t_h_@_U_S_C_-_I_S_I_Q_._A_R_P_A> + + Or + + S: VRFY Jones + R: 550 String does not match anything. + + Or + + S: VRFY Jones + R: 551 User not local; please try <_J_o_n_e_s_@_U_S_C_-_I_S_I_Q_._A_R_P_A> + + Or + + S: VRFY Gourzenkyinplatz + R: 553 User ambiguous. + + Example 3 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + The case of expanding a mailbox list requires a multiline reply as + shown in example 4. + + ------------------------------------------------------------- + + Example of Expanding a Mailing List + + Either + + S: EXPN Example-People + R: 250-Jon Postel <_P_o_s_t_e_l_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 250-Fred Fonebone <_F_o_n_e_b_o_n_e_@_U_S_C_-_I_S_I_Q_._A_R_P_A> + R: 250-Sam Q. Smith <_S_Q_S_m_i_t_h_@_U_S_C_-_I_S_I_Q_._A_R_P_A> + R: 250-Quincy Smith <@USC-ISIF.ARPA:_Q_-_S_m_i_t_h_@_I_S_I_-_V_A_X_A_._A_R_P_A> + R: 250-<_j_o_e_@_f_o_o_-_u_n_i_x_._A_R_P_A> + R: 250 <_x_y_z_@_b_a_r_-_u_n_i_x_._A_R_P_A> + + Or + + S: EXPN Executive-Washroom-List + R: 550 Access Denied to You. + + Example 4 + + ------------------------------------------------------------- + + The character string arguments of the VRFY and EXPN commands + cannot be further restricted due to the variety of implementations + of the user name and mailbox list concepts. On some systems it + may be appropriate for the argument of the EXPN command to be a + file name for a file containing a mailing list, but again there is + a variety of file naming conventions in the Internet. + + The VRFY and EXPN commands are not included in the minimum + implementation (Section 4.5.1), and are not required to work + across relays when they are implemented. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 3.4. SENDING AND MAILING + + The main purpose of SMTP is to deliver messages to user's + mailboxes. A very similar service provided by some hosts is to + deliver messages to user's terminals (provided the user is active + on the host). The delivery to the user's mailbox is called + "mailing", the delivery to the user's terminal is called + "sending". Because in many hosts the implementation of sending is + nearly identical to the implementation of mailing these two + functions are combined in SMTP. However the sending commands are + not included in the required minimum implementation + (Section 4.5.1). Users should have the ability to control the + writing of messages on their terminals. Most hosts permit the + users to accept or refuse such messages. + + The following three command are defined to support the sending + options. These are used in the mail transaction instead of the + MAIL command and inform the receiver-SMTP of the special semantics + of this transaction: + + SEND <SP> FROM:<reverse-path> <CRLF> + + The SEND command requires that the mail data be delivered to + the user's terminal. If the user is not active (or not + accepting terminal messages) on the host a 450 reply may + returned to a RCPT command. The mail transaction is + successful if the message is delivered the terminal. + + SOML <SP> FROM:<reverse-path> <CRLF> + + The Send Or MaiL command requires that the mail data be + delivered to the user's terminal if the user is active (and + accepting terminal messages) on the host. If the user is + not active (or not accepting terminal messages) then the + mail data is entered into the user's mailbox. The mail + transaction is successful if the message is delivered either + to the terminal or the mailbox. + + SAML <SP> FROM:<reverse-path> <CRLF> + + The Send And MaiL command requires that the mail data be + delivered to the user's terminal if the user is active (and + accepting terminal messages) on the host. In any case the + mail data is entered into the user's mailbox. The mail + transaction is successful if the message is delivered the + mailbox. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + The same reply codes that are used for the MAIL commands are used + for these commands. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 3.5. OPENING AND CLOSING + + At the time the transmission channel is opened there is an + exchange to ensure that the hosts are communicating with the hosts + they think they are. + + The following two commands are used in transmission channel + opening and closing: + + HELO <SP> <domain> <CRLF> + + QUIT <CRLF> + + In the HELO command the host sending the command identifies + itself; the command may be interpreted as saying "Hello, I am + <domain>". + + ------------------------------------------------------------- + + Example of Connection Opening + + R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready + S: HELO USC-ISIF.ARPA + R: 250 BBN-UNIX.ARPA + + Example 5 + + ------------------------------------------------------------- + + ------------------------------------------------------------- + + Example of Connection Closing + + S: QUIT + R: 221 BBN-UNIX.ARPA Service closing transmission channel + + Example 6 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + 3.6. RELAYING + + The forward-path may be a source route of the form + "@ONE,@TWO:JOE@THREE", where ONE, TWO, and THREE are hosts. This + form is used to emphasize the distinction between an address and a + route. The mailbox is an absolute address, and the route is + information about how to get there. The two concepts should not + be confused. + + Conceptually the elements of the forward-path are moved to the + reverse-path as the message is relayed from one server-SMTP to + another. The reverse-path is a reverse source route, (i.e., a + source route from the current location of the message to the + originator of the message). When a server-SMTP deletes its + identifier from the forward-path and inserts it into the + reverse-path, it must use the name it is known by in the + environment it is sending into, not the environment the mail came + from, in case the server-SMTP is known by different names in + different environments. + + If when the message arrives at an SMTP the first element of the + forward-path is not the identifier of that SMTP the element is not + deleted from the forward-path and is used to determine the next + SMTP to send the message to. In any case, the SMTP adds its own + identifier to the reverse-path. + + Using source routing the receiver-SMTP receives mail to be relayed + to another server-SMTP The receiver-SMTP may accept or reject the + task of relaying the mail in the same way it accepts or rejects + mail for a local user. The receiver-SMTP transforms the command + arguments by moving its own identifier from the forward-path to + the beginning of the reverse-path. The receiver-SMTP then becomes + a sender-SMTP, establishes a transmission channel to the next SMTP + in the forward-path, and sends it the mail. + + The first host in the reverse-path should be the host sending the + SMTP commands, and the first host in the forward-path should be + the host receiving the SMTP commands. + + Notice that the forward-path and reverse-path appear in the SMTP + commands and replies, but not necessarily in the message. That + is, there is no need for these paths and especially this syntax to + appear in the "To:" , "From:", "CC:", etc. fields of the message + header. + + If a server-SMTP has accepted the task of relaying the mail and + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + later finds that the forward-path is incorrect or that the mail + cannot be delivered for whatever reason, then it must construct an + "undeliverable mail" notification message and send it to the + originator of the undeliverable mail (as indicated by the + reverse-path). + + This notification message must be from the server-SMTP at this + host. Of course, server-SMTPs should not send notification + messages about problems with notification messages. One way to + prevent loops in error reporting is to specify a null reverse-path + in the MAIL command of a notification message. When such a + message is relayed it is permissible to leave the reverse-path + null. A MAIL command with a null reverse-path appears as follows: + + MAIL FROM:<> + + An undeliverable mail notification message is shown in example 7. + This notification is in response to a message originated by JOE at + HOSTW and sent via HOSTX to HOSTY with instructions to relay it on + to HOSTZ. What we see in the example is the transaction between + HOSTY and HOSTX, which is the first step in the return of the + notification message. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + ------------------------------------------------------------- + + Example Undeliverable Mail Notification Message + + S: MAIL FROM:<> + R: 250 ok + S: RCPT TO:<@HOSTX.ARPA:_J_O_E_@_H_O_S_T_W_._A_R_P_A> + R: 250 ok + S: DATA + R: 354 send the mail data, end with . + S: Date: 23 Oct 81 11:22:33 + S: From: _S_M_T_P_@_H_O_S_T_Y_._A_R_P_A + S: To: _J_O_E_@_H_O_S_T_W_._A_R_P_A + S: Subject: Mail System Problem + S: + S: Sorry JOE, your message to _S_A_M_@_H_O_S_T_Z_._A_R_P_A lost. + S: HOSTZ.ARPA said this: + S: "550 No Such User" + S: . + R: 250 ok + + Example 7 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 3.7. DOMAINS + + Domains are a recently introduced concept in the ARPA Internet + mail system. The use of domains changes the address space from a + flat global space of simple character string host names to a + hierarchically structured rooted tree of global addresses. The + host name is replaced by a domain and host designator which is a + sequence of domain element strings separated by periods with the + understanding that the domain elements are ordered from the most + specific to the most general. + + For example, "USC-ISIF.ARPA", "Fred.Cambridge.UK", and + "PC7.LCS.MIT.ARPA" might be host-and-domain identifiers. + + Whenever domain names are used in SMTP only the official names are + used, the use of nicknames or aliases is not allowed. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + 3.8. CHANGING ROLES + + The TURN command may be used to reverse the roles of the two + programs communicating over the transmission channel. + + If program-A is currently the sender-SMTP and it sends the TURN + command and receives an ok reply (250) then program-A becomes the + receiver-SMTP. + + If program-B is currently the receiver-SMTP and it receives the + TURN command and sends an ok reply (250) then program-B becomes + the sender-SMTP. + + To refuse to change roles the receiver sends the 502 reply. + + Please note that this command is optional. It would not normally + be used in situations where the transmission channel is TCP. + However, when the cost of establishing the transmission channel is + high, this command may be quite useful. For example, this command + may be useful in supporting be mail exchange using the public + switched telephone system as a transmission channel, especially if + some hosts poll other hosts for mail exchanges. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + +4. THE SMTP SPECIFICATIONS + + 4.1. SMTP COMMANDS + + 4.1.1. COMMAND SEMANTICS + + The SMTP commands define the mail transfer or the mail system + function requested by the user. SMTP commands are character + strings terminated by <CRLF>. The command codes themselves are + alphabetic characters terminated by <SP> if parameters follow + and <CRLF> otherwise. The syntax of mailboxes must conform to + receiver site conventions. The SMTP commands are discussed + below. The SMTP replies are discussed in the Section 4.2. + + A mail transaction involves several data objects which are + communicated as arguments to different commands. The + reverse-path is the argument of the MAIL command, the + forward-path is the argument of the RCPT command, and the mail + data is the argument of the DATA command. These arguments or + data objects must be transmitted and held pending the + confirmation communicated by the end of mail data indication + which finalizes the transaction. The model for this is that + distinct buffers are provided to hold the types of data + objects, that is, there is a reverse-path buffer, a + forward-path buffer, and a mail data buffer. Specific commands + cause information to be appended to a specific buffer, or cause + one or more buffers to be cleared. + + HELLO (HELO) + + This command is used to identify the sender-SMTP to the + receiver-SMTP. The argument field contains the host name of + the sender-SMTP. + + The receiver-SMTP identifies itself to the sender-SMTP in + the connection greeting reply, and in the response to this + command. + + This command and an OK reply to it confirm that both the + sender-SMTP and the receiver-SMTP are in the initial state, + that is, there is no transaction in progress and all state + tables and buffers are cleared. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + MAIL (MAIL) + + This command is used to initiate a mail transaction in which + the mail data is delivered to one or more mailboxes. The + argument field contains a reverse-path. + + The reverse-path consists of an optional list of hosts and + the sender mailbox. When the list of hosts is present, it + is a "reverse" source route and indicates that the mail was + relayed through each host on the list (the first host in the + list was the most recent relay). This list is used as a + source route to return non-delivery notices to the sender. + As each relay host adds itself to the beginning of the list, + it must use its name as known in the IPCE to which it is + relaying the mail rather than the IPCE from which the mail + came (if they are different). In some types of error + reporting messages (for example, undeliverable mail + notifications) the reverse-path may be null (see Example 7). + + This command clears the reverse-path buffer, the + forward-path buffer, and the mail data buffer; and inserts + the reverse-path information from this command into the + reverse-path buffer. + + RECIPIENT (RCPT) + + This command is used to identify an individual recipient of + the mail data; multiple recipients are specified by multiple + use of this command. + + The forward-path consists of an optional list of hosts and a + required destination mailbox. When the list of hosts is + present, it is a source route and indicates that the mail + must be relayed to the next host on the list. If the + receiver-SMTP does not implement the relay function it may + user the same reply it would for an unknown local user + (550). + + When mail is relayed, the relay host must remove itself from + the beginning forward-path and put itself at the beginning + of the reverse-path. When mail reaches its ultimate + destination (the forward-path contains only a destination + mailbox), the receiver-SMTP inserts it into the destination + mailbox in accordance with its host mail conventions. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + For example, mail received at relay host A with arguments + + FROM:<_U_S_E_R_X_@_H_O_S_T_Y_._A_R_P_A> + TO:<@HOSTA.ARPA,@HOSTB.ARPA:_U_S_E_R_C_@_H_O_S_T_D_._A_R_P_A> + + will be relayed on to host B with arguments + + FROM:<@HOSTA.ARPA:_U_S_E_R_X_@_H_O_S_T_Y_._A_R_P_A> + TO:<@HOSTB.ARPA:_U_S_E_R_C_@_H_O_S_T_D_._A_R_P_A>. + + This command causes its forward-path argument to be appended + to the forward-path buffer. + + DATA (DATA) + + The receiver treats the lines following the command as mail + data from the sender. This command causes the mail data + from this command to be appended to the mail data buffer. + The mail data may contain any of the 128 ASCII character + codes. + + The mail data is terminated by a line containing only a + period, that is the character sequence "<CRLF>.<CRLF>" (see + Section 4.5.2 on Transparency). This is the end of mail + data indication. + + The end of mail data indication requires that the receiver + must now process the stored mail transaction information. + This processing consumes the information in the reverse-path + buffer, the forward-path buffer, and the mail data buffer, + and on the completion of this command these buffers are + cleared. If the processing is successful the receiver must + send an OK reply. If the processing fails completely the + receiver must send a failure reply. + + When the receiver-SMTP accepts a message either for relaying + or for final delivery it inserts at the beginning of the + mail data a time stamp line. The time stamp line indicates + the identity of the host that sent the message, and the + identity of the host that received the message (and is + inserting this time stamp), and the date and time the + message was received. Relayed messages will have multiple + time stamp lines. + + When the receiver-SMTP makes the "final delivery" of a + message it inserts at the beginning of the mail data a + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + return path line. The return path line preserves the + information in the <reverse-path> from the MAIL command. + Here, final delivery means the message leaves the SMTP + world. Normally, this would mean it has been delivered to + the destination user, but in some cases it may be further + processed and transmitted by another mail system. + + It is possible for the mailbox in the return path be + different from the actual sender's mailbox, for example, + if error responses are to be delivered a special error + handling mailbox rather than the message senders. + + The preceding two paragraphs imply that the final mail data + will begin with a return path line, followed by one or more + time stamp lines. These lines will be followed by the mail + data header and body [2]. See Example 8. + + Special mention is needed of the response and further action + required when the processing following the end of mail data + indication is partially successful. This could arise if + after accepting several recipients and the mail data, the + receiver-SMTP finds that the mail data can be successfully + delivered to some of the recipients, but it cannot be to + others (for example, due to mailbox space allocation + problems). In such a situation, the response to the DATA + command must be an OK reply. But, the receiver-SMTP must + compose and send an "undeliverable mail" notification + message to the originator of the message. Either a single + notification which lists all of the recipients that failed + to get the message, or separate notification messages must + be sent for each failed recipient (see Example 7). All + undeliverable mail notification messages are sent using the + MAIL command (even if they result from processing a SEND, + SOML, or SAML command). + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + ------------------------------------------------------------- + + Example of Return Path and Received Time Stamps + + Return-Path: <@GHI.ARPA,@DEF.ARPA,@ABC.ARPA:_J_O_E_@_A_B_C_._A_R_P_A> + Received: from GHI.ARPA by JKL.ARPA ; 27 Oct 81 15:27:39 PST + Received: from DEF.ARPA by GHI.ARPA ; 27 Oct 81 15:15:13 PST + Received: from ABC.ARPA by DEF.ARPA ; 27 Oct 81 15:01:59 PST + Date: 27 Oct 81 15:01:01 PST + From: _J_O_E_@_A_B_C_._A_R_P_A + Subject: Improved Mailing System Installed + To: _S_A_M_@_J_K_L_._A_R_P_A + + This is to inform you that ... + + Example 8 + + ------------------------------------------------------------- + + SEND (SEND) + + This command is used to initiate a mail transaction in which + the mail data is delivered to one or more terminals. The + argument field contains a reverse-path. This command is + successful if the message is delivered to a terminal. + + The reverse-path consists of an optional list of hosts and + the sender mailbox. When the list of hosts is present, it + is a "reverse" source route and indicates that the mail was + relayed through each host on the list (the first host in the + list was the most recent relay). This list is used as a + source route to return non-delivery notices to the sender. + As each relay host adds itself to the beginning of the list, + it must use its name as known in the IPCE to which it is + relaying the mail rather than the IPCE from which the mail + came (if they are different). + + This command clears the reverse-path buffer, the + forward-path buffer, and the mail data buffer; and inserts + the reverse-path information from this command into the + reverse-path buffer. + + SEND OR MAIL (SOML) + + This command is used to initiate a mail transaction in which + the mail data is delivered to one or more terminals or + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + mailboxes. For each recipient the mail data is delivered to + the recipient's terminal if the recipient is active on the + host (and accepting terminal messages), otherwise to the + recipient's mailbox. The argument field contains a + reverse-path. This command is successful if the message is + delivered to a terminal or the mailbox. + + The reverse-path consists of an optional list of hosts and + the sender mailbox. When the list of hosts is present, it + is a "reverse" source route and indicates that the mail was + relayed through each host on the list (the first host in the + list was the most recent relay). This list is used as a + source route to return non-delivery notices to the sender. + As each relay host adds itself to the beginning of the list, + it must use its name as known in the IPCE to which it is + relaying the mail rather than the IPCE from which the mail + came (if they are different). + + This command clears the reverse-path buffer, the + forward-path buffer, and the mail data buffer; and inserts + the reverse-path information from this command into the + reverse-path buffer. + + SEND AND MAIL (SAML) + + This command is used to initiate a mail transaction in which + the mail data is delivered to one or more terminals and + mailboxes. For each recipient the mail data is delivered to + the recipient's terminal if the recipient is active on the + host (and accepting terminal messages), and for all + recipients to the recipient's mailbox. The argument field + contains a reverse-path. This command is successful if the + message is delivered to the mailbox. + + The reverse-path consists of an optional list of hosts and + the sender mailbox. When the list of hosts is present, it + is a "reverse" source route and indicates that the mail was + relayed through each host on the list (the first host in the + list was the most recent relay). This list is used as a + source route to return non-delivery notices to the sender. + As each relay host adds itself to the beginning of the list, + it must use its name as known in the IPCE to which it is + relaying the mail rather than the IPCE from which the mail + came (if they are different). + + This command clears the reverse-path buffer, the + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + forward-path buffer, and the mail data buffer; and inserts + the reverse-path information from this command into the + reverse-path buffer. + + RESET (RSET) + + This command specifies that the current mail transaction is + to be aborted. Any stored sender, recipients, and mail data + must be discarded, and all buffers and state tables cleared. + The receiver must send an OK reply. + + VERIFY (VRFY) + + This command asks the receiver to confirm that the argument + identifies a user. If it is a user name, the full name of + the user (if known) and the fully specified mailbox are + returned. + + This command has no effect on any of the reverse-path + buffer, the forward-path buffer, or the mail data buffer. + + EXPAND (EXPN) + + This command asks the receiver to confirm that the argument + identifies a mailing list, and if so, to return the + membership of that list. The full name of the users (if + known) and the fully specified mailboxes are returned in a + multiline reply. + + This command has no effect on any of the reverse-path + buffer, the forward-path buffer, or the mail data buffer. + + HELP (HELP) + + This command causes the receiver to send helpful information + to the sender of the HELP command. The command may take an + argument (e.g., any command name) and return more specific + information as a response. + + This command has no effect on any of the reverse-path + buffer, the forward-path buffer, or the mail data buffer. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + NOOP (NOOP) + + This command does not affect any parameters or previously + entered commands. It specifies no action other than that + the receiver send an OK reply. + + This command has no effect on any of the reverse-path + buffer, the forward-path buffer, or the mail data buffer. + + QUIT (QUIT) + + This command specifies that the receiver must send an OK + reply, and then close the transmission channel. + + The receiver should not close the transmission channel until + it receives and replies to a QUIT command (even if there was + an error). The sender should not close the transmission + channel until it send a QUIT command and receives the reply + (even if there was an error response to a previous command). + If the connection is closed prematurely the receiver should + act as if a RSET command had been received (canceling any + pending transaction, but not undoing any previously + completed transaction), the sender should act as if the + command or transaction in progress had received a temporary + error (4xx). + + TURN (TURN) + + This command specifies that the receiver must either (1) + send an OK reply and then take on the role of the + sender-SMTP, or (2) send a refusal reply and retain the role + of the receiver-SMTP. + + If program-A is currently the sender-SMTP and it sends the + TURN command and receives an OK reply (250) then program-A + becomes the receiver-SMTP. Program-A is then in the initial + state as if the transmission channel just opened, and it + then sends the 220 service ready greeting. + + If program-B is currently the receiver-SMTP and it receives + the TURN command and sends an OK reply (250) then program-B + becomes the sender-SMTP. Program-B is then in the initial + state as if the transmission channel just opened, and it + then expects to receive the 220 service ready greeting. + + To refuse to change roles the receiver sends the 502 reply. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + There are restrictions on the order in which these command may + be used. + + The first command in a session must be the HELO command. + The HELO command may be used later in a session as well. If + the HELO command argument is not acceptable a 501 failure + reply must be returned and the receiver-SMTP must stay in + the same state. + + The NOOP, HELP, EXPN, and VRFY commands can be used at any + time during a session. + + The MAIL, SEND, SOML, or SAML commands begin a mail + transaction. Once started a mail transaction consists of + one of the transaction beginning commands, one or more RCPT + commands, and a DATA command, in that order. A mail + transaction may be aborted by the RSET command. There may + be zero or more transactions in a session. + + If the transaction beginning command argument is not + acceptable a 501 failure reply must be returned and the + receiver-SMTP must stay in the same state. If the commands + in a transaction are out of order a 503 failure reply must + be returned and the receiver-SMTP must stay in the same + state. + + The last command in a session must be the QUIT command. The + QUIT command can not be used at any other time in a session. + + 4.1.2. COMMAND SYNTAX + + The commands consist of a command code followed by an argument + field. Command codes are four alphabetic characters. Upper + and lower case alphabetic characters are to be treated + identically. Thus, any of the following may represent the mail + command: + + MAIL Mail mail MaIl mAIl + + This also applies to any symbols representing parameter values, + such as "TO" or "to" for the forward-path. Command codes and + the argument fields are separated by one or more spaces. + However, within the reverse-path and forward-path arguments + case is important. In particular, in some hosts the user + "smith" is different from the user "Smith". + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + The argument field consists of a variable length character + string ending with the character sequence <CRLF>. The receiver + is to take no action until this sequence is received. + + Square brackets denote an optional argument field. If the + option is not taken, the appropriate default is implied. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + The following are the SMTP commands: + + HELO <SP> <domain> <CRLF> + + MAIL <SP> FROM:<reverse-path> <CRLF> + + RCPT <SP> TO:<forward-path> <CRLF> + + DATA <CRLF> + + RSET <CRLF> + + SEND <SP> FROM:<reverse-path> <CRLF> + + SOML <SP> FROM:<reverse-path> <CRLF> + + SAML <SP> FROM:<reverse-path> <CRLF> + + VRFY <SP> <string> <CRLF> + + EXPN <SP> <string> <CRLF> + + HELP [<SP> <string>] <CRLF> + + NOOP <CRLF> + + QUIT <CRLF> + + TURN <CRLF> + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + The syntax of the above argument fields (using BNF notation + where applicable) is given below. The "..." notation indicates + that a field may be repeated one or more times. + + <reverse-path> ::= <path> + + <forward-path> ::= <path> + + <path> ::= "<" [ <a-d-l> ":" ] <mailbox> ">" + + <a-d-l> ::= <at-domain> | <at-domain> "," <a-d-l> + + <at-domain> ::= "@" <domain> + + <domain> ::= <element> | <element> "." <domain> + + <element> ::= <name> | "#" <number> | "[" <dotnum> "]" + + <mailbox> ::= <local-part> "@" <domain> + + <local-part> ::= <dot-string> | <quoted-string> + + <name> ::= <a> <ldh-str> <let-dig> + + <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> + + <let-dig> ::= <a> | <d> + + <let-dig-hyp> ::= <a> | <d> | "-" + + <dot-string> ::= <string> | <string> "." <dot-string> + + <string> ::= <char> | <char> <string> + + <quoted-string> ::= """ <qtext> """ + + <qtext> ::= "\" <x> | "\" <x> <qtext> | <q> | <q> <qtext> + + <char> ::= <c> | "\" <x> + + <dotnum> ::= <snum> "." <snum> "." <snum> "." <snum> + + <number> ::= <d> | <d> <number> + + <CRLF> ::= <CR> <LF> + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + <CR> ::= the carriage return character (ASCII code 13) + + <LF> ::= the line feed character (ASCII code 10) + + <SP> ::= the space character (ASCII code 32) + + <snum> ::= one, two, or three digits representing a decimal + integer value in the range 0 through 255 + + <a> ::= any one of the 52 alphabetic characters A through Z + in upper case and a through z in lower case + + <c> ::= any one of the 128 ASCII characters, but not any + <special> or <SP> + + <d> ::= any one of the ten digits 0 through 9 + + <q> ::= any one of the 128 ASCII characters except <CR>, + <LF>, quote ("), or backslash (\) + + <x> ::= any one of the 128 ASCII characters (no exceptions) + + <special> ::= "<" | ">" | "(" | ")" | "[" | "]" | "\" | "." + | "," | ";" | ":" | "@" """ | the control + characters (ASCII codes 0 through 31 inclusive and + 127) + + Note that the backslash, "\", is a quote character, which is + used to indicate that the next character is to be used + literally (instead of its normal interpretation). For example, + "Joe\,Smith" could be used to indicate a single nine character + user field with comma being the fourth character of the field. + + Hosts are generally known by names which are translated to + addresses in each host. Note that the name elements of domains + are the official names -- no use of nicknames or aliases is + allowed. + + Sometimes a host is not known to the translation function and + communication is blocked. To bypass this barrier two numeric + forms are also allowed for host "names". One form is a decimal + integer prefixed by a pound sign, "#", which indicates the + number is the address of the host. Another form is four small + decimal integers separated by dots and enclosed by brackets, + e.g., "[123.255.37.2]", which indicates a 32-bit ARPA Internet + Address in four 8-bit fields. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + The time stamp line and the return path line are formally + defined as follows: + + <return-path-line> ::= "Return-Path:" <SP><reverse-path><CRLF> + + <time-stamp-line> ::= "Received:" <SP> <stamp> <CRLF> + + <stamp> ::= <from-domain> <by-domain> <opt-info> ";" + <daytime> + + <from-domain> ::= "FROM" <SP> <domain> <SP> + + <by-domain> ::= "BY" <SP> <domain> <SP> + + <opt-info> ::= [<via>] [<with>] [<id>] [<for>] + + <via> ::= "VIA" <SP> <link> <SP> + + <with> ::= "WITH" <SP> <protocol> <SP> + + <id> ::= "ID" <SP> <string> <SP> + + <for> ::= "FOR" <SP> <path> <SP> + + <link> ::= The standard names for links are registered with + the Network Information Center. + + <protocol> ::= The standard names for protocols are + registered with the Network Information Center. + + <daytime> ::= <SP> <date> <SP> <time> + + <date> ::= <dd> <SP> <mon> <SP> <yy> + + <time> ::= <hh> ":" <mm> ":" <ss> <SP> <zone> + + <dd> ::= the one or two decimal integer day of the month in + the range 1 to 31. + + <mon> ::= "JAN" | "FEB" | "MAR" | "APR" | "MAY" | "JUN" | + "JUL" | "AUG" | "SEP" | "OCT" | "NOV" | "DEC" + + <yy> ::= the two decimal integer year of the century in the + range 00 to 99. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + <hh> ::= the two decimal integer hour of the day in the + range 00 to 24. + + <mm> ::= the two decimal integer minute of the hour in the + range 00 to 59. + + <ss> ::= the two decimal integer second of the minute in the + range 00 to 59. + + <zone> ::= "UT" for Universal Time (the default) or other + time zone designator (as in [2]). + + ------------------------------------------------------------- + + Return Path Example + + Return-Path: <@CHARLIE.ARPA,@BAKER.ARPA:_J_O_E_@_A_B_L_E_._A_R_P_A> + + Example 9 + + ------------------------------------------------------------- + + ------------------------------------------------------------- + + Time Stamp Line Example + + Received: FROM ABC.ARPA BY XYZ.ARPA ; 22 OCT 81 09:23:59 PDT + + Received: from ABC.ARPA by XYZ.ARPA via TELENET with X25 + id M12345 for _S_m_i_t_h_@_P_D_Q_._A_R_P_A ; 22 OCT 81 09:23:59 PDT + + Example 10 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + 4.2. SMTP REPLIES + + Replies to SMTP commands are devised to ensure the synchronization + of requests and actions in the process of mail transfer, and to + guarantee that the sender-SMTP always knows the state of the + receiver-SMTP. Every command must generate exactly one reply. + + The details of the command-reply sequence are made explicit in + Section 5.3 on Sequencing and Section 5.4 State Diagrams. + + An SMTP reply consists of a three digit number (transmitted as + three alphanumeric characters) followed by some text. The number + is intended for use by automata to determine what state to enter + next; the text is meant for the human user. It is intended that + the three digits contain enough encoded information that the + sender-SMTP need not examine the text and may either discard it or + pass it on to the user, as appropriate. In particular, the text + may be receiver-dependent and context dependent, so there are + likely to be varying texts for each reply code. A discussion of + the theory of reply codes is given in Appendix E. Formally, a + reply is defined to be the sequence: a three-digit code, <SP>, + one line of text, and <CRLF>, or a multiline reply (as defined in + Appendix E). Only the EXPN and HELP commands are expected to + result in multiline replies in normal circumstances, however + multiline replies are allowed for any command. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 4.2.1. REPLY CODES BY FUNCTION GROUPS + + 500 Syntax error, command unrecognized + [This may include errors such as command line too long] + 501 Syntax error in parameters or arguments + 502 Command not implemented + 503 Bad sequence of commands + 504 Command parameter not implemented + + 211 System status, or system help reply + 214 Help message + [Information on how to use the receiver or the meaning of a + particular non-standard command; this reply is useful only + to the human user] + + 220 <domain> Service ready + 221 <domain> Service closing transmission channel + 421 <domain> Service not available, + closing transmission channel + [This may be a reply to any command if the service knows it + must shut down] + + 250 Requested mail action okay, completed + 251 User not local; will forward to <forward-path> + 450 Requested mail action not taken: mailbox unavailable + [E.g., mailbox busy] + 550 Requested action not taken: mailbox unavailable + [E.g., mailbox not found, no access] + 451 Requested action aborted: error in processing + 551 User not local; please try <forward-path> + 452 Requested action not taken: insufficient system storage + 552 Requested mail action aborted: exceeded storage allocation + 553 Requested action not taken: mailbox name not allowed + [E.g., mailbox syntax incorrect] + 354 Start mail input; end with <CRLF>.<CRLF> + 554 Transaction failed + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + 4.2.2. NUMERIC ORDER LIST OF REPLY CODES + + 211 System status, or system help reply + 214 Help message + [Information on how to use the receiver or the meaning of a + particular non-standard command; this reply is useful only + to the human user] + 220 <domain> Service ready + 221 <domain> Service closing transmission channel + 250 Requested mail action okay, completed + 251 User not local; will forward to <forward-path> + + 354 Start mail input; end with <CRLF>.<CRLF> + + 421 <domain> Service not available, + closing transmission channel + [This may be a reply to any command if the service knows it + must shut down] + 450 Requested mail action not taken: mailbox unavailable + [E.g., mailbox busy] + 451 Requested action aborted: local error in processing + 452 Requested action not taken: insufficient system storage + + 500 Syntax error, command unrecognized + [This may include errors such as command line too long] + 501 Syntax error in parameters or arguments + 502 Command not implemented + 503 Bad sequence of commands + 504 Command parameter not implemented + 550 Requested action not taken: mailbox unavailable + [E.g., mailbox not found, no access] + 551 User not local; please try <forward-path> + 552 Requested mail action aborted: exceeded storage allocation + 553 Requested action not taken: mailbox name not allowed + [E.g., mailbox syntax incorrect] + 554 Transaction failed + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 4.3. SEQUENCING OF COMMANDS AND REPLIES + + The communication between the sender and receiver is intended to + be an alternating dialogue, controlled by the sender. As such, + the sender issues a command and the receiver responds with a + reply. The sender must wait for this response before sending + further commands. + + One important reply is the connection greeting. Normally, a + receiver will send a 220 "Service ready" reply when the connection + is completed. The sender should wait for this greeting message + before sending any commands. + + Note: all the greeting type replies have the official name of + the server host as the first word following the reply code. + + For example, + + 220 <SP> USC-ISIF.ARPA <SP> Service ready <CRLF> + + The table below lists alternative success and failure replies for + each command. These must be strictly adhered to; a receiver may + substitute text in the replies, but the meaning and action implied + by the code numbers and by the specific command reply sequence + cannot be altered. + + COMMAND-REPLY SEQUENCES + + Each command is listed with its possible replies. The prefixes + used before the possible replies are "P" for preliminary (not + used in SMTP), "I" for intermediate, "S" for success, "F" for + failure, and "E" for error. The 421 reply (service not + available, closing transmission channel) may be given to any + command if the SMTP-receiver knows it must shut down. This + listing forms the basis for the State Diagrams in Section 4.4. + + CONNECTION ESTABLISHMENT + S: 220 + F: 421 + HELO + S: 250 + E: 500, 501, 504, 421 + MAIL + S: 250 + F: 552, 451, 452 + E: 500, 501, 421 + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + RCPT + S: 250, 251 + F: 550, 551, 552, 553, 450, 451, 452 + E: 500, 501, 503, 421 + DATA + I: 354 -> data -> S: 250 + F: 552, 554, 451, 452 + F: 451, 554 + E: 500, 501, 503, 421 + RSET + S: 250 + E: 500, 501, 504, 421 + SEND + S: 250 + F: 552, 451, 452 + E: 500, 501, 502, 421 + SOML + S: 250 + F: 552, 451, 452 + E: 500, 501, 502, 421 + SAML + S: 250 + F: 552, 451, 452 + E: 500, 501, 502, 421 + VRFY + S: 250, 251 + F: 550, 551, 553 + E: 500, 501, 502, 504, 421 + EXPN + S: 250 + F: 550 + E: 500, 501, 502, 504, 421 + HELP + S: 211, 214 + E: 500, 501, 502, 504, 421 + NOOP + S: 250 + E: 500, 421 + QUIT + S: 221 + E: 500 + TURN + S: 250 + F: 502 + E: 500, 503 + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 4.4. STATE DIAGRAMS + + Following are state diagrams for a simple-minded SMTP + implementation. Only the first digit of the reply codes is used. + There is one state diagram for each group of SMTP commands. The + command groupings were determined by constructing a model for each + command and then collecting together the commands with + structurally identical models. + + For each command there are three possible outcomes: "success" + (S), "failure" (F), and "error" (E). In the state diagrams below + we use the symbol B for "begin", and the symbol W for "wait for + reply". + + First, the diagram that represents most of the SMTP commands: + + 1,3 +---+ + ----------->| E | + | +---+ + | + +---+ cmd +---+ 2 +---+ + | B |---------->| W |---------->| S | + +---+ +---+ +---+ + | + | 4,5 +---+ + ----------->| F | + +---+ + + This diagram models the commands: + + HELO, MAIL, RCPT, RSET, SEND, SOML, SAML, VRFY, EXPN, HELP, + NOOP, QUIT, TURN. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + A more complex diagram models the DATA command: + + +---+ DATA +---+ 1,2 +---+ + | B |---------->| W |-------------------->| E | + +---+ +---+ ------------>+---+ + 3| |4,5 | + | | | + -------------- ----- | + | | | +---+ + | ---------- -------->| S | + | | | | +---+ + | | ------------ + | | | | + V 1,3| |2 | + +---+ data +---+ --------------->+---+ + | |---------->| W | | F | + +---+ +---+-------------------->+---+ + 4,5 + + Note that the "data" here is a series of lines sent from the + sender to the receiver with no response expected until the last + line is sent. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + 4.5. DETAILS + + 4.5.1. MINIMUM IMPLEMENTATION + + In order to make SMTP workable, the following minimum + implementation is required for all receivers: + + COMMANDS -- HELO + MAIL + RCPT + DATA + RSET + NOOP + QUIT + + 4.5.2. TRANSPARENCY + + Without some provision for data transparency the character + sequence "<CRLF>.<CRLF>" ends the mail text and cannot be sent + by the user. In general, users are not aware of such + "forbidden" sequences. To allow all user composed text to be + transmitted transparently the following procedures are used. + + 1. Before sending a line of mail text the sender-SMTP checks + the first character of the line. If it is a period, one + additional period is inserted at the beginning of the line. + + 2. When a line of mail text is received by the receiver-SMTP + it checks the line. If the line is composed of a single + period it is the end of mail. If the first character is a + period and there are other characters on the line, the first + character is deleted. + + The mail data may contain any of the 128 ASCII characters. All + characters are to be delivered to the recipient's mailbox + including format effectors and other control characters. If + the transmission channel provides an 8-bit byte (octets) data + stream, the 7-bit ASCII codes are transmitted right justified + in the octets with the high order bits cleared to zero. + + In some systems it may be necessary to transform the data as + it is received and stored. This may be necessary for hosts + that use a different character set than ASCII as their local + character set, or that store data in records rather than + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + strings. If such transforms are necessary, they must be + reversible -- especially if such transforms are applied to + mail being relayed. + + 4.5.3. SIZES + + There are several objects that have required minimum maximum + sizes. That is, every implementation must be able to receive + objects of at least these sizes, but must not send objects + larger than these sizes. + + **************************************************** + * * + * TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION * + * TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH * + * OF THESE OBJECTS SHOULD BE USED. * + * * + **************************************************** + + user + + The maximum total length of a user name is 64 characters. + + domain + + The maximum total length of a domain name or number is 64 + characters. + + path + + The maximum total length of a reverse-path or + forward-path is 256 characters (including the punctuation + and element separators). + + command line + + The maximum total length of a command line including the + command word and the <CRLF> is 512 characters. + + reply line + + The maximum total length of a reply line including the + reply code and the <CRLF> is 512 characters. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + text line + + The maximum total length of a text line including the + <CRLF> is 1000 characters (but not counting the leading + dot duplicated for transparency). + + recipients buffer + + The maximum total number of recipients that must be + buffered is 100 recipients. + + **************************************************** + * * + * TO THE MAXIMUM EXTENT POSSIBLE, IMPLEMENTATION * + * TECHNIQUES WHICH IMPOSE NO LIMITS ON THE LENGTH * + * OF THESE OBJECTS SHOULD BE USED. * + * * + **************************************************** + + Errors due to exceeding these limits may be reported by using + the reply codes, for example: + + 500 Line too long. + + 501 Path too long + + 552 Too many recipients. + + 552 Too much mail data. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +APPENDIX A + + TCP Transport service + + The Transmission Control Protocol [3] is used in the ARPA + Internet, and in any network following the US DoD standards for + internetwork protocols. + + Connection Establishment + + The SMTP transmission channel is a TCP connection established + between the sender process port U and the receiver process port + L. This single full duplex connection is used as the + transmission channel. This protocol is assigned the service + port 25 (31 octal), that is L=25. + + Data Transfer + + The TCP connection supports the transmission of 8-bit bytes. + The SMTP data is 7-bit ASCII characters. Each character is + transmitted as an 8-bit byte with the high-order bit cleared to + zero. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + +APPENDIX B + + NCP Transport service + + The ARPANET Host-to-Host Protocol [4] (implemented by the Network + Control Program) may be used in the ARPANET. + + Connection Establishment + + The SMTP transmission channel is established via NCP between + the sender process socket U and receiver process socket L. The + Initial Connection Protocol [5] is followed resulting in a pair + of simplex connections. This pair of connections is used as + the transmission channel. This protocol is assigned the + contact socket 25 (31 octal), that is L=25. + + Data Transfer + + The NCP data connections are established in 8-bit byte mode. + The SMTP data is 7-bit ASCII characters. Each character is + transmitted as an 8-bit byte with the high-order bit cleared to + zero. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +APPENDIX C + + NITS + + The Network Independent Transport Service [6] may be used. + + Connection Establishment + + The SMTP transmission channel is established via NITS between + the sender process and receiver process. The sender process + executes the CONNECT primitive, and the waiting receiver + process executes the ACCEPT primitive. + + Data Transfer + + The NITS connection supports the transmission of 8-bit bytes. + The SMTP data is 7-bit ASCII characters. Each character is + transmitted as an 8-bit byte with the high-order bit cleared to + zero. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + +APPENDIX D + + X.25 Transport service + + It may be possible to use the X.25 service [7] as provided by the + Public Data Networks directly, however, it is suggested that a + reliable end-to-end protocol such as TCP be used on top of X.25 + connections. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +APPENDIX E + + Theory of Reply Codes + + The three digits of the reply each have a special significance. + The first digit denotes whether the response is good, bad or + incomplete. An unsophisticated sender-SMTP will be able to + determine its next action (proceed as planned, redo, retrench, + etc.) by simply examining this first digit. A sender-SMTP that + wants to know approximately what kind of error occurred (e.g., + mail system error, command syntax error) may examine the second + digit, reserving the third digit for the finest gradation of + information. + + There are five values for the first digit of the reply code: + + 1yz Positive Preliminary reply + + The command has been accepted, but the requested action + is being held in abeyance, pending confirmation of the + information in this reply. The sender-SMTP should send + another command specifying whether to continue or abort + the action. + + [Note: SMTP does not have any commands that allow this + type of reply, and so does not have the continue or + abort commands.] + + 2yz Positive Completion reply + + The requested action has been successfully completed. A + new request may be initiated. + + 3yz Positive Intermediate reply + + The command has been accepted, but the requested action + is being held in abeyance, pending receipt of further + information. The sender-SMTP should send another command + specifying this information. This reply is used in + command sequence groups. + + 4yz Transient Negative Completion reply + + The command was not accepted and the requested action did + not occur. However, the error condition is temporary and + the action may be requested again. The sender should + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + return to the beginning of the command sequence (if any). + It is difficult to assign a meaning to "transient" when + two different sites (receiver- and sender- SMTPs) must + agree on the interpretation. Each reply in this category + might have a different time value, but the sender-SMTP is + encouraged to try again. A rule of thumb to determine if + a reply fits into the 4yz or the 5yz category (see below) + is that replies are 4yz if they can be repeated without + any change in command form or in properties of the sender + or receiver. (E.g., the command is repeated identically + and the receiver does not put up a new implementation.) + + 5yz Permanent Negative Completion reply + + The command was not accepted and the requested action did + not occur. The sender-SMTP is discouraged from repeating + the exact request (in the same sequence). Even some + "permanent" error conditions can be corrected, so the + human user may want to direct the sender-SMTP to + reinitiate the command sequence by direct action at some + point in the future (e.g., after the spelling has been + changed, or the user has altered the account status). + + The second digit encodes responses in specific categories: + + x0z Syntax -- These replies refer to syntax errors, + syntactically correct commands that don't fit any + functional category, and unimplemented or superfluous + commands. + + x1z Information -- These are replies to requests for + information, such as status or help. + + x2z Connections -- These are replies referring to the + transmission channel. + + x3z Unspecified as yet. + + x4z Unspecified as yet. + + x5z Mail system -- These replies indicate the status of + the receiver mail system vis-a-vis the requested + transfer or other mail system action. + + The third digit gives a finer gradation of meaning in each + category specified by the second digit. The list of replies + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + illustrates this. Each reply text is recommended rather than + mandatory, and may even change according to the command with + which it is associated. On the other hand, the reply codes + must strictly follow the specifications in this section. + Receiver implementations should not invent new codes for + slightly different situations from the ones described here, but + rather adapt codes already defined. + + For example, a command such as NOOP whose successful execution + does not offer the sender-SMTP any new information will return + a 250 reply. The response is 502 when the command requests an + unimplemented non-site-specific action. A refinement of that + is the 504 reply for a command that is implemented, but that + requests an unimplemented parameter. + + The reply text may be longer than a single line; in these cases + the complete text must be marked so the sender-SMTP knows when it + can stop reading the reply. This requires a special format to + indicate a multiple line reply. + + The format for multiline replies requires that every line, + except the last, begin with the reply code, followed + immediately by a hyphen, "-" (also known as minus), followed by + text. The last line will begin with the reply code, followed + immediately by <SP>, optionally some text, and <CRLF>. + + For example: + 123-First line + 123-Second line + 123-234 text beginning with numbers + 123 The last line + + In many cases the sender-SMTP then simply needs to search for + the reply code followed by <SP> at the beginning of a line, and + ignore all preceding lines. In a few cases, there is important + data for the sender in the reply "text". The sender will know + these cases from the current context. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + +APPENDIX F + + Scenarios + + This section presents complete scenarios of several types of SMTP + sessions. + + A Typical SMTP Transaction Scenario + + This SMTP example shows mail sent by Smith at host USC-ISIF, to + Jones, Green, and Brown at host BBN-UNIX. Here we assume that + host USC-ISIF contacts host BBN-UNIX directly. The mail is + accepted for Jones and Brown. Green does not have a mailbox at + host BBN-UNIX. + + ------------------------------------------------------------- + + R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready + S: HELO USC-ISIF.ARPA + R: 250 BBN-UNIX.ARPA + + S: MAIL FROM:<_S_m_i_t_h_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_J_o_n_e_s_@_B_B_N_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_G_r_e_e_n_@_B_B_N_-_U_N_I_X_._A_R_P_A> + R: 550 No such user here + + S: RCPT TO:<_B_r_o_w_n_@_B_B_N_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 BBN-UNIX.ARPA Service closing transmission channel + + Scenario 1 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + Aborted SMTP Transaction Scenario + + ------------------------------------------------------------- + + R: 220 MIT-Multics.ARPA Simple Mail Transfer Service Ready + S: HELO ISI-VAXA.ARPA + R: 250 MIT-Multics.ARPA + + S: MAIL FROM:<_S_m_i_t_h_@_I_S_I_-_V_A_X_A_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_J_o_n_e_s_@_M_I_T_-_M_u_l_t_i_c_s_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_G_r_e_e_n_@_M_I_T_-_M_u_l_t_i_c_s_._A_R_P_A> + R: 550 No such user here + + S: RSET + R: 250 OK + + S: QUIT + R: 221 MIT-Multics.ARPA Service closing transmission channel + + Scenario 2 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Relayed Mail Scenario + + ------------------------------------------------------------- + + Step 1 -- Source Host to Relay Host + + R: 220 USC-ISIE.ARPA Simple Mail Transfer Service Ready + S: HELO MIT-AI.ARPA + R: 250 USC-ISIE.ARPA + + S: MAIL FROM:<_J_Q_P_@_M_I_T_-_A_I_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<@USC-ISIE.ARPA:_J_o_n_e_s_@_B_B_N_-_V_A_X_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Date: 2 Nov 81 22:33:44 + S: From: John Q. Public <_J_Q_P_@_M_I_T_-_A_I_._A_R_P_A> + S: Subject: The Next Meeting of the Board + S: To: _J_o_n_e_s_@_B_B_N_-_V_a_x_._A_R_P_A + S: + S: Bill: + S: The next meeting of the board of directors will be + S: on Tuesday. + S: John. + S: . + R: 250 OK + + S: QUIT + R: 221 USC-ISIE.ARPA Service closing transmission channel + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + Step 2 -- Relay Host to Destination Host + + R: 220 BBN-VAX.ARPA Simple Mail Transfer Service Ready + S: HELO USC-ISIE.ARPA + R: 250 BBN-VAX.ARPA + + S: MAIL FROM:<@USC-ISIE.ARPA:_J_Q_P_@_M_I_T_-_A_I_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_J_o_n_e_s_@_B_B_N_-_V_A_X_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Received: from MIT-AI.ARPA by USC-ISIE.ARPA ; + 2 Nov 81 22:40:10 UT + S: Date: 2 Nov 81 22:33:44 + S: From: John Q. Public <_J_Q_P_@_M_I_T_-_A_I_._A_R_P_A> + S: Subject: The Next Meeting of the Board + S: To: _J_o_n_e_s_@_B_B_N_-_V_a_x_._A_R_P_A + S: + S: Bill: + S: The next meeting of the board of directors will be + S: on Tuesday. + S: John. + S: . + R: 250 OK + + S: QUIT + R: 221 USC-ISIE.ARPA Service closing transmission channel + + Scenario 3 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Verifying and Sending Scenario + + ------------------------------------------------------------- + + R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready + S: HELO MIT-MC.ARPA + R: 250 SU-SCORE.ARPA + + S: VRFY Crispin + R: 250 Mark Crispin <_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + + S: SEND FROM:<_E_A_K_@_M_I_T_-_M_C_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 SU-SCORE.ARPA Service closing transmission channel + + Scenario 4 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + Sending and Mailing Scenarios + + First the user's name is verified, then an attempt is made to + send to the user's terminal. When that fails, the messages is + mailed to the user's mailbox. + + ------------------------------------------------------------- + + R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready + S: HELO MIT-MC.ARPA + R: 250 SU-SCORE.ARPA + + S: VRFY Crispin + R: 250 Mark Crispin <_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + + S: SEND FROM:<_E_A_K_@_M_I_T_-_M_C_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + R: 450 User not active now + + S: RSET + R: 250 OK + + S: MAIL FROM:<_E_A_K_@_M_I_T_-_M_C_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 SU-SCORE.ARPA Service closing transmission channel + + Scenario 5 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Doing the preceding scenario more efficiently. + + ------------------------------------------------------------- + + R: 220 SU-SCORE.ARPA Simple Mail Transfer Service Ready + S: HELO MIT-MC.ARPA + R: 250 SU-SCORE.ARPA + + S: VRFY Crispin + R: 250 Mark Crispin <_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + + S: SOML FROM:<_E_A_K_@_M_I_T_-_M_C_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_A_d_m_i_n_._M_R_C_@_S_U_-_S_C_O_R_E_._A_R_P_A> + R: 250 User not active now, so will do mail. + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 SU-SCORE.ARPA Service closing transmission channel + + Scenario 6 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + Mailing List Scenario + + First each of two mailing lists are expanded in separate sessions + with different hosts. Then the message is sent to everyone that + appeared on either list (but no duplicates) via a relay host. + + ------------------------------------------------------------- + + Step 1 -- Expanding the First List + + R: 220 MIT-AI.ARPA Simple Mail Transfer Service Ready + S: HELO SU-SCORE.ARPA + R: 250 MIT-AI.ARPA + + S: EXPN Example-People + R: 250-<_A_B_C_@_M_I_T_-_M_C_._A_R_P_A> + R: 250-Fred Fonebone <_F_o_n_e_b_o_n_e_@_U_S_C_-_I_S_I_Q_._A_R_P_A> + R: 250-Xenon Y. Zither <_X_Y_Z_@_M_I_T_-_A_I_._A_R_P_A> + R: 250-Quincy Smith <@USC-ISIF.ARPA:_Q_-_S_m_i_t_h_@_I_S_I_-_V_A_X_A_._A_R_P_A> + R: 250-<_j_o_e_@_f_o_o_-_u_n_i_x_._A_R_P_A> + R: 250 <_x_y_z_@_b_a_r_-_u_n_i_x_._A_R_P_A> + + S: QUIT + R: 221 MIT-AI.ARPA Service closing transmission channel + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Step 2 -- Expanding the Second List + + R: 220 MIT-MC.ARPA Simple Mail Transfer Service Ready + S: HELO SU-SCORE.ARPA + R: 250 MIT-MC.ARPA + + S: EXPN Interested-Parties + R: 250-Al Calico <_A_B_C_@_M_I_T_-_M_C_._A_R_P_A> + R: 250-<_X_Y_Z_@_M_I_T_-_A_I_._A_R_P_A> + R: 250-Quincy Smith <@USC-ISIF.ARPA:_Q_-_S_m_i_t_h_@_I_S_I_-_V_A_X_A_._A_R_P_A> + R: 250-<_f_r_e_d_@_B_B_N_-_U_N_I_X_._A_R_P_A> + R: 250 <_x_y_z_@_b_a_r_-_u_n_i_x_._A_R_P_A> + + S: QUIT + R: 221 MIT-MC.ARPA Service closing transmission channel + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + Step 3 -- Mailing to All via a Relay Host + + R: 220 USC-ISIE.ARPA Simple Mail Transfer Service Ready + S: HELO SU-SCORE.ARPA + R: 250 USC-ISIE.ARPA + + S: MAIL FROM:<_A_c_c_o_u_n_t_._P_e_r_s_o_n_@_S_U_-_S_C_O_R_E_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_A_B_C_@_M_I_T_-_M_C_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_F_o_n_e_b_o_n_e_@_U_S_C_-_I_S_I_Q_A_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_X_Y_Z_@_M_I_T_-_A_I_._A_R_P_A> + R: 250 OK + S: RCPT + TO:<@USC-ISIE.ARPA,@USC-ISIF.ARPA:_Q_-_S_m_i_t_h_@_I_S_I_-_V_A_X_A_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_j_o_e_@_F_O_O_-_U_N_I_X_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_x_y_z_@_B_A_R_-_U_N_I_X_._A_R_P_A> + R: 250 OK + S: RCPT TO:<@USC-ISIE.ARPA:_f_r_e_d_@_B_B_N_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 USC-ISIE.ARPA Service closing transmission channel + + Scenario 7 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Forwarding Scenarios + + ------------------------------------------------------------- + + R: 220 USC-ISIF.ARPA Simple Mail Transfer Service Ready + S: HELO LBL-UNIX.ARPA + R: 250 USC-ISIF.ARPA + + S: MAIL FROM:<_m_o_@_L_B_L_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_f_r_e_d_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 251 User not local; will forward to <_J_o_n_e_s_@_U_S_C_-_I_S_I_._A_R_P_A> + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 USC-ISIF.ARPA Service closing transmission channel + + Scenario 8 + + ------------------------------------------------------------- + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + ------------------------------------------------------------- + + Step 1 -- Trying the Mailbox at the First Host + + R: 220 USC-ISIF.ARPA Simple Mail Transfer Service Ready + S: HELO LBL-UNIX.ARPA + R: 250 USC-ISIF.ARPA + + S: MAIL FROM:<_m_o_@_L_B_L_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_f_r_e_d_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 251 User not local; will forward to <_J_o_n_e_s_@_U_S_C_-_I_S_I_._A_R_P_A> + + S: RSET + R: 250 OK + + S: QUIT + R: 221 USC-ISIF.ARPA Service closing transmission channel + + Step 2 -- Delivering the Mail at the Second Host + + R: 220 USC-ISI.ARPA Simple Mail Transfer Service Ready + S: HELO LBL-UNIX.ARPA + R: 250 USC-ISI.ARPA + + S: MAIL FROM:<_m_o_@_L_B_L_-_U_N_I_X_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_J_o_n_e_s_@_U_S_C_-_I_S_I_._A_R_P_A> + R: OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 USC-ISI.ARPA Service closing transmission channel + + Scenario 9 + + ------------------------------------------------------------- + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + Too Many Recipients Scenario + + ------------------------------------------------------------- + + R: 220 BERKELEY.ARPA Simple Mail Transfer Service Ready + S: HELO USC-ISIF.ARPA + R: 250 BERKELEY.ARPA + + S: MAIL FROM:<_P_o_s_t_e_l_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_f_a_b_r_y_@_B_E_R_K_E_L_E_Y_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_e_r_i_c_@_B_E_R_K_E_L_E_Y_._A_R_P_A> + R: 552 Recipient storage full, try again in another transaction + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: MAIL FROM:<_P_o_s_t_e_l_@_U_S_C_-_I_S_I_F_._A_R_P_A> + R: 250 OK + + S: RCPT TO:<_e_r_i_c_@_B_E_R_K_E_L_E_Y_._A_R_P_A> + R: 250 OK + + S: DATA + R: 354 Start mail input; end with <CRLF>.<CRLF> + S: Blah blah blah... + S: ...etc. etc. etc. + S: . + R: 250 OK + + S: QUIT + R: 221 BERKELEY.ARPA Service closing transmission channel + + Scenario 10 + + ------------------------------------------------------------- + + Note that a real implementation must handle many recipients as + specified in Section 4.5.3. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + +GLOSSARY + + ASCII + + American Standard Code for Information Interchange [1]. + + command + + A request for a mail service action sent by the sender-SMTP to the + receiver-SMTP. + + domain + + The hierarchially structured global character string address of a + host computer in the mail system. + + end of mail data indication + + A special sequence of characters that indicates the end of the + mail data. In particular, the five characters carriage return, + line feed, period, carriage return, line feed, in that order. + + host + + A computer in the internetwork environment on which mailboxes or + SMTP processes reside. + + line + + A a sequence of ASCII characters ending with a <CRLF>. + + mail data + + A sequence of ASCII characters of arbitrary length, which conforms + to the standard set in the Standard for the Format of ARPA + Internet Text Messages (_R_F_C_ _8_2_2 [2]). + + mailbox + + A character string (address) which identifies a user to whom mail + is to be sent. Mailbox normally consists of the host and user + specifications. The standard mailbox naming convention is defined + to be "user@domain". Additionally, the "container" in which mail + is stored. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + + receiver-SMTP process + + A process which transfers mail in cooperation with a sender-SMTP + process. It waits for a connection to be established via the + transport service. It receives SMTP commands from the + sender-SMTP, sends replies, and performs the specified operations. + + reply + + A reply is an acknowledgment (positive or negative) sent from + receiver to sender via the transmission channel in response to a + command. The general form of a reply is a completion code + (including error codes) followed by a text string. The codes are + for use by programs and the text is usually intended for human + users. + + sender-SMTP process + + A process which transfers mail in cooperation with a receiver-SMTP + process. A local language may be used in the user interface + command/reply dialogue. The sender-SMTP initiates the transport + service connection. It initiates SMTP commands, receives replies, + and governs the transfer of mail. + + session + + The set of exchanges that occur while the transmission channel is + open. + + transaction + + The set of exchanges required for one message to be transmitted + for one or more recipients. + + transmission channel + + A full-duplex communication path between a sender-SMTP and a + receiver-SMTP for the exchange of commands, replies, and mail + text. + + transport service + + Any reliable stream-oriented data communication services. For + example, NCP, TCP, NITS. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + user + + A human being (or a process on behalf of a human being) wishing to + obtain mail transfer service. In addition, a recipient of + computer mail. + + word + + A sequence of printing characters. + + <CRLF> + + The characters carriage return and line feed (in that order). + + <SP> + + The space character. + +_R_F_C_ _8_2_1 August 1982 + Simple Mail Transfer Protocol + +REFERENCES + + [1] ASCII + + ASCII, "USA Code for Information Interchange", United States of + America Standards Institute, X3.4, 1968. Also in: Feinler, E. + and J. Postel, eds., "ARPANET Protocol Handbook", NIC 7104, for + the Defense Communications Agency by SRI International, Menlo + Park, California, Revised January 1978. + + [2] _R_F_C_ _8_2_2 + + Crocker, D., "Standard for the Format of ARPA Internet Text + Messages," _R_F_C_ _8_2_2, Department of Electrical Engineering, + University of Delaware, August 1982. + + [3] TCP + + Postel, J., ed., "Transmission Control Protocol - DARPA Internet + Program Protocol Specification", _R_F_C_ _7_9_3, USC/Information Sciences + Institute, NTIS AD Number A111091, September 1981. Also in: + Feinler, E. and J. Postel, eds., "Internet Protocol Transition + Workbook", SRI International, Menlo Park, California, March 1982. + + [4] NCP + + McKenzie,A., "Host/Host Protocol for the ARPA Network", NIC 8246, + January 1972. Also in: Feinler, E. and J. Postel, eds., "ARPANET + Protocol Handbook", NIC 7104, for the Defense Communications + Agency by SRI International, Menlo Park, California, Revised + January 1978. + + [5] Initial Connection Protocol + + Postel, J., "Official Initial Connection Protocol", NIC 7101, + 11 June 1971. Also in: Feinler, E. and J. Postel, eds., "ARPANET + Protocol Handbook", NIC 7104, for the Defense Communications + Agency by SRI International, Menlo Park, California, Revised + January 1978. + + [6] NITS + + PSS/SG3, "A Network Independent Transport Service", Study Group 3, + The Post Office PSS Users Group, February 1980. Available from + the DCPU, National Physical Laboratory, Teddington, UK. + +August 1982 _R_F_C_ _8_2_1 +Simple Mail Transfer Protocol + + [7] X.25 + + CCITT, "Recommendation X.25 - Interface Between Data Terminal + Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for + Terminals Operating in the Packet Mode on Public Data Networks," + CCITT Orange Book, Vol. VIII.2, International Telephone and + Telegraph Consultative Committee, Geneva, 1976. + +Comments about this RFC: + * _R_F_C_ _8_2_1_:_ _w_h_e_r_e_ _i_ _c_a_n_ _w_r_i_t_e_ _m_y_ _s_c_r_i_p_t_s by mahmood (1/31/2004) + * _R_F_C_ _8_2_1_:_ _A_ _r_o_n_a_l_d_ _r_ _d_a_v_i_s_ _o_n_ _p_a_r_o_l_e_ _h_a_s_ _h_a_c_k_e_d_ _i_n_t_o_ _m_y_ _a_c_c_o_u_n_t_._ _h_e_ _i_s_ _n_o_t + _s_u_p_p_o_s_s_e_d_ _t_o_._._. by lifeisunfair (12/20/2006) + * _R_F_C_ _8_2_1_:_ _I_ _a_m_ _u_n_a_b_l_e_ _t_o_ _s_e_n_d_ _o_u_t_ _e_-_m_a_i_l_s_._T_h_e_ _e_r_r_o_r_ _m_e_s_s_a_g_e_ _s_a_y_s_:_ _T_h_e + _m_e_s_s_a_g_e_ _c_o_u_l_d_ _n_o_t_ _b_e_._._. by nita (11/5/2004) + * _R_F_C_ _8_2_1_:_ _H_o_w_ _c_a_n_ _I_ _c_r_e_a_t_e_ _a_ _s_c_r_i_p_t_ _d_o_ _r_u_n_ _o_n_ _W_i_n_d_o_w_s_ _?_ _?_ _?_ _I_'_d_ _l_i_k_e_ _t_o + _u_s_e_ _a_ _s_c_r_i_p_t_._._. by Marcelo (11/8/2004) + * _R_F_C_ _8_2_1_:_ _h_o_w_ _s_m_t_p_ _w_o_r_k_s_ _i_n_ _e_x_c_h_a_n_g_e_ _s_y_t_e_m_? by saif (12/4/2005) + * _R_F_C_ _8_2_1_:_ _V_e_r_y_ _G_o_o_d_ _B_u_t_ _I_ _W_a_n_t_ _C_o_d_i_n_g_ _o_f_ _S_i_m_l_e_ _M_a_i_l_ _t_r_a_n_s_f_e_r_ _p_r_o_t_o_c_o_l by + Ankit Pahuja (3/23/2006) + * _R_F_C_ _8_2_1_:_ _T_h_i_s_ _R_F_C_ _i_s_ _o_b_s_o_l_e_t_e_d_ _b_y_ _R_F_C_2_8_2_1_._ _A_n_y_o_n_e_ _s_e_e_k_i_n_g_ _t_o_ _u_n_d_e_r_s_t_a_n_d + _m_o_d_e_r_n_ _S_M_T_P_ _o_r_._._. by William Cole (4/23/2005) + * _R_F_C_ _8_2_1_:_ _C_a_n_ _I_ _a_t_t_a_c_h_ _a_ _f_i_l_e_ _t_o_ _a_n_ _o_u_t_g_o_i_n_g_ _e_-_m_a_i_l_ _o_n_ _t_h_e_ _m_a_i_n_f_r_a_m_e_? by + dphill06 (5/23/2006) + * _R_F_C_ _8_2_1_:_ _I_ _w_a_n_t_ _t_o_ _g_e_t_ _t_h_e_ _i_n_f_o_r_m_a_t_i_o_n_ _o_f_ _u_t_l___s_m_t_p by eagle_hawk (6/2/ + 2005) + * _R_F_C_ _8_2_1_:_ _I_ _a_m_ _a_ _M_A_C_ _u_s_e_r_ _w_h_o_ _w_a_s_ _p_r_o_v_i_d_e_d_ _a_n_ _s_m_p_t_ _c_a_p_a_b_i_l_i_t_y_ _w_h_i_c_h_ _I_ _c_a_n + _n_o_t_ _u_s_e_ _f_o_r_ _l_a_c_k_._._. by Larry Stolurow (6/22/2006) + * _R_F_C_ _8_2_1_:_ _A_l_w_a_y_s_ _a_ _g_o_o_d_ _r_e_a_d_!_I_ _i_m_p_l_e_m_e_n_t_ _S_M_T_P_ _o_v_e_r_ _V_B_6_ _W_i_n_s_o_c_k_._ _W_o_r_k_s + _g_r_e_a_t_,_ _r_e_f_e_r_ _t_o_._._. by python_kiss (11/3/2005) + * _R_F_C_ _8_2_1_:_ _v_e_r_y_ _s_i_m_p_l_e_ _t_o_ _c_o_n_f_i_g_u_r_e by dixson (3/26/2007) + * _R_F_C_ _8_2_1_:_ _R_F_C_ _8_2_1_ _d_o_e_s_ _n_o_t_ _c_o_m_m_e_n_t_ _o_n_ _t_h_e_ _v_a_l_i_d_i_t_y_ _o_f_ _t_r_a_i_l_i_n_g_ _d_o_t_s_ _f_o_r + _d_o_m_a_i_n_ _n_a_m_e_s_._ _I_t_._._. by Brett (12/22/2004) + * _R_F_C_ _8_2_1_:_ _W_h_a_t_ _i_s_ _R_F_C_ _f_o_r_m_a_t_?_H_o_ _i_t_ _i_s_ _u_s_e_d_? by siva (3/2/2004) + * _R_F_C_ _8_2_1_:_ _s_i_r_,_w_e_ _a_r_e_ _d_o_i_n_g_ _p_r_o_j_e_c_t_ _o_n_ _S_M_S_ _f_r_o_m_ _m_o_b_i_l_e_ _t_o_ _i_n_t_e_r_n_e_t_._S_o_ _f_o_r + _c_o_m_m_u_n_i_c_a_t_i_n_g_w_i_t_h_._._. by Krishna (5/9/2004) + * _R_F_C_ _8_2_1_:_ _H_i_!_ _V_e_r_y_ _n_i_c_e_ _s_i_t_e_!_ _T_h_a_n_k_s_ _y_o_u_ _v_e_r_y_ _m_u_c_h_!_ _m_8_8_C_X_f_G_F_N_X_H_O_k_S by + rzq9PUrVNv (1/21/2007) + * _R_F_C_ _8_2_1_:_ _i_ _n_e_e_t_ _s_l_e_e_p_ _p_f_f_f_f_f_f_ _w_a_t_ _i_ _n_e_e_ _t_e_ _d_o_e by goldface (9/24/2005) + +Previous: _R_F_C_ _0_8_2_0_ _-_ _A_s_s_i_g_n_e_d_ _n_u_m_b_e_r_s Next: _R_F_C_ _0_8_2_2_ _-_ _S_T_A_N_D_A_R_D_ _F_O_R_ _T_H_E + _F_O_R_M_A_T_ _O_F_ _A_R_P_A_ _I_N_T_E_R_N_E_T_ _T_E_X_T_ _M_E_S_S_A_G_E_S + +=============================================================================== + [ _R_F_C_ _I_n_d_e_x | _R_F_C_ _S_e_a_r_c_h | _U_s_e_n_e_t_ _F_A_Q_s | _W_e_b_ _F_A_Q_s | _D_o_c_u_m_e_n_t_s | _C_i_t_i_e_s ] + 2008 FAQS.ORG. All rights reserved. + diff --git a/src/Makefile b/src/Makefile @@ -0,0 +1,10 @@ +all: +# gcc muxin.c -o muxin + gcc -Wall pop3.c -o dmc-pop3 + gcc -Wall imap4.c -o dmc-imap4 + +clean: + rm -f dmc-pop3 dmc-imap4 + +loc: + sloccount . diff --git a/src/dmc b/src/dmc @@ -0,0 +1,10 @@ +#!/bin/sh +# +# Dynamic Mail Client +# + +FIFO=fifo-session +./dmc-pop3 $FIFO | nc localhost 110 | ./dmc-pop3 > $FIFO + +./dmc-pop3 | nc localhost 110 | ./dmc-pop3-post +./dmc-imap4 | openssl s_client -host radare.org -port 993 | ./dmc-imap4 diff --git a/src/imap4.c b/src/imap4.c @@ -0,0 +1,107 @@ +/* dmc :: Copyleft -- pancake (at) nopcode (dot) org */ + +#include <stdio.h> +#include <string.h> +#include <stdlib.h> + +static char word[1024]; +static int ctr = 1; + +static char *getword() { + fscanf(stdin, "%127s", word); + if (feof(stdin)) + *word = '\0'; + return word; +} + +static int waitreply() { + char *str; + int ret = -1; + fgets(word, sizeof(word), stdin); + if (atoi(word) != ctr-1) + fprintf(stderr, "Invalid sequence number received\n"); + if ( (str = strchr(word, ' ')) ) { + if (!memcmp(str+1, "OK", 3)) + ret = 1; + else if (!memcmp(str+1, "NO", 4)) + ret = 0; + } + return ret; // 1 if true, 0 if false +} + +#if 0 +LIST - list all folders +LSUB - list all subscribed folders +SUBSCRIBE - subcribe a folder +CHECK - ??? +CLOSE - commit the delete stuff (maybe must be done after rm) +EXPUNGE - permanent remove of deltec +SEARCH - ... +RECENT - show the number of recent messages +#endif +static int doword(char *word) { + int ret = 1; + if (*word == '\0' || !strcmp(word, "exit")) { + printf("%d LOGOUT\n", ctr++); + waitreply(); + ret = 0; + } else + if (!strcmp(word, "help") || !strcmp(word, "?")) { + fprintf(stderr, "Use: ls lsdir cat head rm rmdir login exit mvdir\n"); + } else + if (!strcmp(word, "ls")) { +// TODO: + printf("LIST\n"); + waitreply(); + } else + if (!strcmp(word, "cd")) { + printf("%d SELECT %s\n", ctr++, getword()); + waitreply(); + } else + if (!strcmp(word, "search")) { + printf("%d SEARCH TEXT \"%s\"\n", ctr++, getword()); + waitreply(); + } else + if (!strcmp(word, "lsdir")) { + printf("%d LIST \"\" *\n", ctr++); + waitreply(); + } else + if (!strcmp(word, "cat")) { + printf("%d FETCH %d ALL\n", + ctr++, atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "head")) { + printf("%d FETCH %d body[header]\n", + ctr++, atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "mvdir")) { + printf("%d RENAME %s %s\n", + ctr++, getword(), getword()); + } else + if (!strcmp(word, "rm")) { +// TODO: + printf("DELE %d\n", atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "rmdir")) { + printf("%d DELETE %d\n", + ctr++, atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "login")) { + printf("%d LOGIN %s %s\n", + ctr++, getword(), getword()); + waitreply(); + } else { + printf("%d NOOP\n", ctr++); + waitreply(); + } + return ret; +} + +int main() { + while(doword(getword())); + return 0; +} diff --git a/src/pop3.c b/src/pop3.c @@ -0,0 +1,93 @@ +/* dmc :: Copyleft -- pancake (at) nopcode (dot) org */ + +#include <stdio.h> +#include <string.h> +#include <signal.h> +#include <stdlib.h> +#include <unistd.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> + + +static char word[1024]; +static char *fifo; +static int ff; + +static char *getword() { + fscanf(stdin, "%255s", word); + if (feof(stdin)) + *word = '\0'; + return word; +} + +static int waitreply() { + int ret = -1; + fflush(stdout); + fgets(word, sizeof(word), stdin); + if (!memcmp(word, "+OK", 3)) + ret = 1; + else + if (!memcmp(word, "-ERR", 4)) + ret = 0; + return ret; // 1 if true, 0 if false +} + +static int doword(char *word) { + int ret = 1; + if (*word == '\0' || !strcmp(word, "exit")) { + printf("QUIT\n"); + waitreply(); + ret = 0; + } else + if (!strcmp(word, "help") || !strcmp(word, "?")) { + fprintf(stderr, "Use: ls cat head rm login exit\n"); + } else + if (!strcmp(word, "ls")) { + printf("LIST\n"); + waitreply(); + } else + if (!strcmp(word, "cat")) { + printf("RETR %d\n", atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "head")) { + printf("TOP %d\n", atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "rm")) { + printf("DELE %d\n", atoi(getword())); + waitreply(); + } else + if (!strcmp(word, "login")) { + printf("USER %s\n", getword()); + printf("PASS %s\n", getword()); + waitreply(); + } else printf("NOOP\n"); + return ret; +} + +static void parseoutput(void) { + while(!feof(stdin)) { + sleep(1); + printf("TODO\n"); + } +} + +static void cleanup(int foo) { + close(ff); + unlink(fifo); + exit(0); +} + +int main(int argc, char **argv) { + if (argc>1) { + signal(SIGINT, cleanup); + fifo = argv[1]; + mkfifo(fifo, 0600); + ff = open(fifo, O_NONBLOCK|O_RDWR); + while(doword(getword())); + cleanup(0); + } else parseoutput(); + return 0; +}