dmc

imap-rfc3501.txt (216452B)

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 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
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 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.
 
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    The limited permissions granted above are perpetual and will not be
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 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)
 
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 _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
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