Network Working Group                                        M. Crispin
Request for Comments: 2060                     University of Washington
Obsoletes: 1730                                           December 1996
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.

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 remote message folders,
   called "mailboxes", in a way that is functionally equivalent to local
   mailboxes.  IMAP4rev1 also provides the capability for an offline
   client to resynchronize with the server (see also [IMAP-DISC]).

   IMAP4rev1 includes operations for creating, deleting, and renaming
   mailboxes; checking for new messages; permanently removing messages;
   setting and clearing flags; [RFC-822] and [MIME-IMB] 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 [ACAP].

   IMAP4rev1 does not specify a means of posting mail; this function is
   handled by a mail transfer protocol such as [SMTP].

   IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
   unpublished IMAP2bis protocols.  In the course of the evolution of
   IMAP4rev1, some aspects in the earlier protocol have become obsolete.
   Obsolete commands, responses, and data formats which an IMAP4rev1
   implementation may encounter when used with an earlier implementation
   are described in [IMAP-OBSOLETE].





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   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.

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
2.      Protocol Overview .........................................    5
2.1.    Link Level ................................................    5
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 ........................................    7
2.3.1.  Message Numbers ...........................................    7
2.3.1.1.        Unique Identifier (UID) Message Attribute .........    7
2.3.1.2.        Message Sequence Number Message Attribute .........    9
2.3.2.  Flags Message Attribute ....................................   9
2.3.3.  Internal Date Message Attribute ...........................   10
2.3.4.  [RFC-822] Size Message Attribute ..........................   11
2.3.5.  Envelope Structure Message Attribute ......................   11
2.3.6.  Body Structure Message Attribute ..........................   11
2.4.    Message Texts .............................................   11
3.      State and Flow Diagram ....................................   11
3.1.    Non-Authenticated State ...................................   11
3.2.    Authenticated State .......................................   11
3.3.    Selected State ............................................   12
3.4.    Logout State ..............................................   12
4.      Data Formats ..............................................   12
4.1.    Atom ......................................................   13
4.2.    Number ....................................................   13
4.3.    String .....................................................  13
4.3.1.  8-bit and Binary Strings ..................................   13
4.4.    Parenthesized List ........................................   14
4.5.    NIL .......................................................   14
5.      Operational Considerations ................................   14
5.1.    Mailbox Naming ............................................   14
5.1.1.  Mailbox Hierarchy Naming ..................................   14
5.1.2.  Mailbox Namespace Naming Convention .......................   14
5.1.3.  Mailbox International Naming Convention ...................   15
5.2.    Mailbox Size and Message Status Updates ...................   16
5.3.    Response when no Command in Progress ......................   16
5.4.    Autologout Timer ..........................................   16
5.5.    Multiple Commands in Progress .............................   17



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6.      Client Commands ...........................................   17
6.1.    Client Commands - Any State ...............................   18
6.1.1.  CAPABILITY Command ........................................   18
6.1.2.  NOOP Command ..............................................   19
6.1.3.  LOGOUT Command ............................................   20
6.2.    Client Commands - Non-Authenticated State .................   20
6.2.1.  AUTHENTICATE Command ......................................   21
6.2.2.  LOGIN Command .............................................   22
6.3.    Client Commands - Authenticated State .....................   22
6.3.1.  SELECT Command ............................................   23
6.3.2.  EXAMINE Command ...........................................   24
6.3.3.  CREATE Command ............................................   25
6.3.4.  DELETE Command ............................................   26
6.3.5.  RENAME Command ............................................   27
6.3.6.  SUBSCRIBE Command .........................................   29
6.3.7.  UNSUBSCRIBE Command .......................................   30
6.3.8.  LIST Command ..............................................   30
6.3.9.  LSUB Command ..............................................   32
6.3.10. STATUS Command ............................................   33
6.3.11. APPEND Command ............................................   34
6.4.    Client Commands - Selected State ..........................   35
6.4.1.  CHECK Command .............................................   36
6.4.2.  CLOSE Command .............................................   36
6.4.3.  EXPUNGE Command ...........................................   37
6.4.4.  SEARCH Command ............................................   37
6.4.5.  FETCH Command .............................................   41
6.4.6.  STORE Command .............................................   45
6.4.7.  COPY Command ..............................................   46
6.4.8.  UID Command ...............................................   47
6.5.    Client Commands - Experimental/Expansion ..................   48
6.5.1.  X<atom> Command ...........................................   48
7.      Server Responses ..........................................   48
7.1.    Server Responses - Status Responses .......................   49
7.1.1.  OK Response ...............................................   51
7.1.2.  NO Response ...............................................   51
7.1.3.  BAD Response ..............................................   52
7.1.4.  PREAUTH Response ..........................................   52
7.1.5.  BYE Response ..............................................   52
7.2.    Server Responses - Server and Mailbox Status ..............   53
7.2.1.  CAPABILITY Response .......................................   53
7.2.2.  LIST Response ..............................................  54
7.2.3.  LSUB Response .............................................   55
7.2.4   STATUS Response ...........................................   55
7.2.5.  SEARCH Response ...........................................   55
7.2.6.  FLAGS Response ............................................   56
7.3.    Server Responses - Mailbox Size ...........................   56
7.3.1.  EXISTS Response ...........................................   56
7.3.2.  RECENT Response ...........................................   57



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7.4.    Server Responses - Message Status .........................   57
7.4.1.  EXPUNGE Response ..........................................   57
7.4.2.  FETCH Response ............................................   58
7.5.    Server Responses - Command Continuation Request ...........   63
8.      Sample IMAP4rev1 connection ...............................   63
9.      Formal Syntax .............................................   64
10.     Author's Note .............................................   74
11.     Security Considerations ...................................   74
12.     Author's Address ..........................................   75
Appendices ........................................................   76
A.      References ................................................   76
B.      Changes from RFC 1730 .....................................   77
C.      Key Word Index ............................................   79


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

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

   The following terms are used in this document to signify the
   requirements of this specification.

   1) MUST, or the adjective REQUIRED, means that the definition is
      an absolute requirement of the specification.

   2) MUST NOT that the definition is an absolute prohibition of the
      specification.




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   3) SHOULD means that there may exist valid reasons in particular
      circumstances to ignore a particular item, but the full
      implications MUST be understood and carefully weighed before
      choosing a different course.

   4) SHOULD NOT means that there may exist valid reasons in
      particular circumstances when the particular behavior is
      acceptable or even useful, but the full implications SHOULD be
      understood and the case carefully weighed before implementing
      any behavior described with this label.

   5) MAY, or the adjective OPTIONAL, means that an item is truly
      optional.  One vendor may choose to include the item because a
      particular marketplace requires it or because the vendor feels
      that it enhances the product while another vendor may omit the
      same item.  An implementation which does not include a
      particular option MUST be prepared to interoperate with another
      implementation which does include the option.

      "Can" is used instead of "may" when referring 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.

2.      Protocol Overview

2.1.    Link Level

   The IMAP4rev1 protocol assumes a reliable data stream such as
   provided by TCP.  When TCP is used, an IMAP4rev1 server listens on
   port 143.




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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.

   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 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.





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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 protocol error such as
   unrecognized command or command syntax error).

   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 may 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 and 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



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   that is permanently guaranteed not to refer to any other message in
   the mailbox.  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.  Unique identifiers also persist across
   sessions.  This permits 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 is a unique identifier validity value,
   which is sent in an UIDVALIDITY response code in an OK untagged
   response at mailbox selection time.  If unique identifiers from an
   earlier session fail to persist to this session, the unique
   identifier validity value MUST be greater than the one used in the
   earlier session.

      Note: 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 identifers are no
      longer strictly ascending as a result of the re-ordering.  Another
      instance in which unique identifiers are regenerated is if the
      message store has no mechanism to store unique identifiers.
      Although this specification recognizes that this may be
      unavoidable in certain server environments, it STRONGLY ENCOURAGES
      message store implementation techniques that avoid this problem.

      Another cause of non-persistance is if the mailbox is deleted and
      a new mailbox with the same name is created at a later date, Since
      the name is the same, a client may not know that this is a new
      mailbox unless the unique identifier validity is different.  A
      good value to use for the unique identifier validity value 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.

   The unique identifier of a message MUST NOT change during the
   session, and SHOULD NOT change between sessions.  However, if it is
   not possible to preserve the unique identifier of a message in a
   subsequent session, each subsequent session MUST have a new unique
   identifier validity value that is larger than any that was used
   previously.




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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.  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 "EXISTS 11" 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 may 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).





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        \Recent     Message is "recently" arrived in this mailbox.  This
                    session is the first session to have been notified
                    about this message; 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-arrives 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 may 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, 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 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 [RFC-822] 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.







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2.3.4.  [RFC-822] Size Message Attribute

   The number of octets in the message, as expressed in [RFC-822]
   format.

2.3.5.  Envelope Structure Message Attribute

   A parsed representation of the [RFC-822] envelope information (not to
   be confused with an [SMTP] envelope) of the message.

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 [RFC-822] text of a
   message, IMAP4rev1 permits the fetching of portions of the full
   message text.  Specifically, it is possible to fetch the [RFC-822]
   message header, [RFC-822] message body, a [MIME-IMB] body part, or a
   [MIME-IMB] header.

3.      State and Flow Diagram

   An IMAP4rev1 server is in one of four states.  Most commands are
   valid in only certain states.  It is a protocol error for the client
   to attempt a command while the command is in an inappropriate state.
   In this case, a server will respond with a BAD or NO (depending upon
   server implementation) command completion result.

3.1.    Non-Authenticated State

   In non-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 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, or after an error in selecting a mailbox.






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3.3.    Selected State

   In 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 logout state, the connection is being terminated, and the server
   will close the connection.  This state can be entered as a result of
   a client request or by unilateral server decision.

            +--------------------------------------+
            |initial connection and server greeting|
            +--------------------------------------+
                      || (1)       || (2)        || (3)
                      VV           ||            ||
            +-----------------+    ||            ||
            |non-authenticated|    ||            ||
            +-----------------+    ||            ||
             || (7)   || (4)       ||            ||
             ||       VV           VV            ||
             ||     +----------------+           ||
             ||     | authenticated  |<=++       ||
             ||     +----------------+  ||       ||
             ||       || (7)   || (5)   || (6)   ||
             ||       ||       VV       ||       ||
             ||       ||    +--------+  ||       ||
             ||       ||    |selected|==++       ||
             ||       ||    +--------+           ||
             ||       ||       || (7)            ||
             VV       VV       VV                VV
            +--------------------------------------+
            |     logout and close 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.



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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: literal and 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 that can be used in a quoted
   string.

   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.









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   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 atom "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 ().

5.      Operational Considerations

5.1.    Mailbox Naming

   The interpretation of mailbox names is implementation-dependent.
   However, the case-insensitive mailbox name INBOX is a special name
   reserved to mean "the primary mailbox for this user on this server".

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.







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      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 an mailbox name of
      "#news.comp.mail.misc", and the name "comp.mail.misc" could refer
      to a different object (e.g. a user's private mailbox).

5.1.3.  Mailbox International Naming Convention

   By convention, international mailbox names are specified using a
   modified version of the UTF-7 encoding described in [UTF-7].  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 chararacters can be
         represented in encoded form.

   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, 0x7f-0xff, and all
   Unicode 16-bit octets) 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.  All names start in US-ASCII, and MUST end in US-ASCII (that
   is, a name that ends with a Unicode 16-bit octet MUST end with a "-
   ").





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      For example, here is a mailbox name which mixes English, Japanese,
      and Chinese text: ~peter/mail/&ZeVnLIqe-/&U,BTFw-

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 mail delivery),
   change the flags of message 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.

   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
   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, that timer MUST be of
   at least 30 minutes' duration.  The receipt of ANY command from the
   client during that interval SHOULD suffice to reset the autologout
   timer.













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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; for example, 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 a 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

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



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   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.

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.  This listing of
      capabilities is not dependent upon connection state or user.  It
      is therefore not necessary to issue a CAPABILITY command more than
      once in a connection.









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      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.

      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 AUTH=KERBEROS_V4
               S: abcd 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.  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




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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 - Non-Authenticated State

   In non-authenticated state, the AUTHENTICATE or LOGIN command
   establishes authentication and enter authenticated state.  The
   AUTHENTICATE command provides a general mechanism for a variety of
   authentication techniques, whereas the LOGIN command uses the
   traditional user name and plaintext password pair.

   Server implementations MAY allow non-authenticated access to certain
   mailboxes.  The convention is to use a LOGIN command with the userid
   "anonymous".  A password is REQUIRED.  It is implementation-dependent
   what requirements, if any, are placed on the password and what access
   restrictions are placed on anonymous users.

   Once authenticated (including as anonymous), it is not possible to
   re-enter non-authenticated state.

   In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
   the following commands are valid in non-authenticated state:
   AUTHENTICATE and LOGIN.












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6.2.1.  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 an authentication mechanism,
      such as described in [IMAP-AUTH], 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 protection mechanism
      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 authentication protocol exchange consists of a series of
      server challenges and client answers 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 answer consists of a line
      consisting of a BASE64 encoded string.  If the client wishes to
      cancel an authentication exchange, it issues a line with a single
      "*".  If the server receives such an answer, it MUST reject the
      AUTHENTICATE command by sending a tagged BAD response.

      A protection mechanism provides integrity and privacy protection
      to the connection.  If a protection mechanism is negotiated, it is
      applied to all subsequent data sent over the connection.  The
      protection mechanism 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.  Once the
      protection mechanism is in effect, the stream of command and
      response octets is processed into buffers of ciphertext.  Each
      buffer is transferred over the connection as a stream of octets
      prepended with a four octet field in network byte order that
      represents the length of the following data.  The maximum
      ciphertext buffer length is defined by the protection mechanism.

      Authentication mechanisms are OPTIONAL.  Protection mechanisms are
      also OPTIONAL; an authentication mechanism MAY be implemented
      without any protection mechanism.  If an AUTHENTICATE command
      fails with a NO response, the client MAY try another



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      authentication mechanism by issuing another AUTHENTICATE command,
      or MAY attempt to authenticate by using the LOGIN command.  In
      other words, the client MAY request authentication types in
      decreasing order of preference, with the LOGIN command as a last
      resort.

   Example:    S: * OK KerberosV4 IMAP4rev1 Server
               C: A001 AUTHENTICATE KERBEROS_V4
               S: + AmFYig==
               C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
                  +nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
                  WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
               S: + or//EoAADZI=
               C: DiAF5A4gA+oOIALuBkAAmw==
               S: A001 OK Kerberos V4 authentication successful

      Note: the line breaks in the first client answer are for editorial
      clarity and are not in real authenticators.

6.2.2.  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.

   Example:    C: a001 LOGIN SMITH SESAME
               S: a001 OK LOGIN completed

6.3.    Client Commands - Authenticated State

   In 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 selected state.

   In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
   the following commands are valid in authenticated state: SELECT,
   EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
   STATUS, and APPEND.





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6.3.1.  SELECT Command

   Arguments:  mailbox name

   Responses:  REQUIRED untagged responses: FLAGS, EXISTS, RECENT
               OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS

   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:

      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 [UIDVALIDITY <n>]
                  The unique identifier validity value.  See the
                  description of the UID command for more detail.

   to define the initial state of the mailbox at the client.

   The server SHOULD also send an UNSEEN response code in an OK
   untagged response, indicating the message sequence number of the
   first unseen message in the mailbox.

   If the client can not change the permanent state of one or more of
   the flags listed in the FLAGS untagged response, the server SHOULD
   send a PERMANENTFLAGS response code in an OK untagged response,
   listing the flags that the client can change permanently.

   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.




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   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: * 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
               OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS

   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.












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      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: * 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
      it.

      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 complete successfully.
      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.



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   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.






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   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



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      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".

      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















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               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 some server sites may 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












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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 \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 a context in which the mailbox
      name is interpreted in an implementation-defined manner.




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      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 null if
      the reference is non-rooted or is null.  In all cases, the
      hierarchy delimiter is returned.  This permits a client to get the
      hierarchy delimiter even when no mailboxes by that name currently
      exist.

      The reference and mailbox name arguments are interpreted, in an
      implementation-dependent fashion, into a canonical form that
      represents an unambiguous left-to-right hierarchy.  The returned
      mailbox names will be in the interpreted form.

      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).



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      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.

      A server MAY validate the subscribed names to see if they still
      exist.  If a name does not exist, it SHOULD be flagged with the
      \Noselect attribute in the LSUB response.  The server MUST NOT



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      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

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.  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.

      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 UID value that will be assigned to a new
                     message in the mailbox.  It is guaranteed that this
                     value will not change unless new messages are added
                     to the mailbox; and that it will change when new
                     messages are added even if those new messages are
                     subsequently expunged.



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      UIDVALIDITY    The unique identifier validity value of the
                     mailbox.

      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 [RFC-822] 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 [RFC-822] 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 empty by default.

   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.






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   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 mail 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}
               C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
               C: From: Fred Foobar <foobar@Blurdybloop.COM>
               C: Subject: afternoon meeting
               C: To: mooch@owatagu.siam.edu
               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 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.






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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
      mail 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
               NO - close failure: no mailbox selected
               BAD - command unknown or arguments invalid

      The CLOSE command permanently removes from the currently selected
      mailbox all messages that have the \Deleted flag set, and returns
      to authenticated state from 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



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      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 from the currently
      selected mailbox all messages that have the \Deleted flag set.
      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






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      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
      [RFC-822]/[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).

      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.

      <message 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.




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      BEFORE <date>  Messages whose internal date 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 [RFC-822]) and that
                     contains the specified string in the [RFC-822]
                     field-body.

      KEYWORD <flag> Messages with the specified keyword set.

      LARGER <n>     Messages with an [RFC-822] 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 is within the
                     specified date.

      OR <search-key1> <search-key2>
                     Messages that match either search key.

      RECENT         Messages that have the \Recent flag set.



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      SEEN           Messages that have the \Seen flag set.

      SENTBEFORE <date>
                     Messages whose [RFC-822] Date: header is earlier
                     than the specified date.

      SENTON <date>  Messages whose [RFC-822] Date: header is within the
                     specified date.

      SENTSINCE <date>
                     Messages whose [RFC-822] Date: header is within or
                     later than the specified date.

      SINCE <date>   Messages whose internal date is within or later
                     than the specified date.

      SMALLER <n>    Messages with an [RFC-822] 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 <message set>
                     Messages with unique identifiers corresponding to
                     the specified unique identifier set.

      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
                     set.

      UNSEEN         Messages that do not have the \Seen flag set.





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   Example:    C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
               S: * SEARCH 2 84 882
               S: A282 OK SEARCH completed

6.4.5.  FETCH Command

   Arguments:  message set
               message data item names

   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.

      The currently defined data items that can be fetched are:

      ALL            Macro equivalent to: (FLAGS INTERNALDATE
                     RFC822.SIZE ENVELOPE)

      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.






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                     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 [RFC-822] 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 [RFC-822]) 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.  In all
                     cases, the delimiting blank line between the header
                     and the body is always included.

                     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 [RFC-822] header.


















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                       Here is an example of a complex message
                       with some of its part specifiers:

                        HEADER     ([RFC-822] header of the message)
                        TEXT       MULTIPART/MIXED
                        1          TEXT/PLAIN
                        2          APPLICATION/OCTET-STREAM
                        3          MESSAGE/RFC822
                        3.HEADER   ([RFC-822] header of the message)
                        3.TEXT     ([RFC-822] text body of the message)
                        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 ([RFC-822] header of the message)
                        4.2.TEXT   ([RFC-822] text body of the message)
                        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.





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                     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 [RFC-822] header and
                     [MIME-IMB] headers.

      ENVELOPE       The envelope structure of the message.  This is
                     computed by the server by parsing the [RFC-822]
                     header into the component parts, defaulting various
                     fields as necessary.

      FAST           Macro equivalent to: (FLAGS INTERNALDATE
                     RFC822.SIZE)

      FLAGS          The flags that are set for this message.

      FULL           Macro equivalent to: (FLAGS INTERNALDATE
                     RFC822.SIZE ENVELOPE BODY)

      INTERNALDATE   The internal date of the message.

      RFC822         Functionally equivalent to BODY[], differing in the
                     syntax of the resulting untagged FETCH data (RFC822
                     is returned).

      RFC822.HEADER  Functionally equivalent to BODY.PEEK[HEADER],
                     differing in the syntax of the resulting untagged
                     FETCH data (RFC822.HEADER is returned).

      RFC822.SIZE    The [RFC-822] size of the message.

      RFC822.TEXT    Functionally equivalent to BODY[TEXT], differing in
                     the syntax of the resulting untagged FETCH data
                     (RFC822.TEXT is returned).

      UID            The unique identifier for the message.








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   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:  message 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 with the
                     argument.  The new value of the flags are 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 are returned as if a FETCH
                     of those flags was done.





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      +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 are 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:  message 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 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.









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      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 message set argument are unique identifiers instead of message
      sequence numbers.

      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 the message sequence number set 1:100 and the
      UID set 443:557.

      Message set ranges are permitted; however, there is no guarantee
      that unique identifiers be contiguous.  A non-existent unique
      identifier within a message set range is ignored without any error
      message generated.

      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.







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   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 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 AUTH=KERBEROS_V4 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.






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   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 selected state.  In 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
   may 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



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   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.

      NEWNAME        Followed by a mailbox name and a new mailbox name.
                     A SELECT or EXAMINE is failing because the target
                     mailbox name no longer exists because it was
                     renamed to the new mailbox name.  This is a hint to
                     the client that the operation can succeed if the
                     SELECT or EXAMINE is reissued with the new mailbox
                     name.

      PARSE          The human-readable text represents an error in
                     parsing the [RFC-822] 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 that 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 reject
                     it with a NO reply or store the state 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.







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      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.

      UIDVALIDITY    Followed by a decimal number, indicates the unique
                     identifier validity value.

      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.



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   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 and
      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






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      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.

   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".

      A capability name which begins with "AUTH=" indicates that the
      server supports that particular authentication mechanism.







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      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.

   Example:    S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4 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 the
      mailbox is "interesting" or not, or if the name is a \Noselect
      name, the server SHOULD NOT send either \Marked or \Unmarked.



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      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









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      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 trasnmitted 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 mail).

      The update from the EXISTS response MUST be recorded by the
      client.

   Example:    S: * 23 EXISTS










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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
      mail).

         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).

      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



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      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.

      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.

                     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



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                     7-bit; 8-bit characters are not permitted in
                     headers.  Note also that the blank line at the end
                     of the header is always included in header data.

                     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 nested
                     body.  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 BASE645-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")
                     "<960723163407.20117h@cac.washington.edu>"
                     "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



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                        "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.  The disposition type and
                        attribute names will be defined in a future
                        standards-track revision to [DISPOSITION].

                     body language
                        A string or parenthesized list giving the body
                        language value as defined in [LANGUAGE-TAGS].

                     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].



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                     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 RFC822
                     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].

                     Any following extension data are not yet defined in
                     this version of the protocol, and would be as
                     described above under multipart extension data.





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      ENVELOPE       A parenthesized list that describes the envelope
                     structure of a message.  This is computed by the
                     server by parsing the [RFC-822] 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.

                     [RFC-822] 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
                     RFC 822 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.

                     Any field of an envelope or address structure that
                     is not applicable is presented as NIL.  Note that
                     the server MUST default the reply-to and sender
                     fields from the from field; a client is not
                     expected to know to do this.

      FLAGS          A parenthesized list of flags that are set for this
                     message.

      INTERNALDATE   A string representing the internal date of the
                     message.

      RFC822         Equivalent to BODY[].

      RFC822.HEADER  Equivalent to BODY.PEEK[HEADER].

      RFC822.SIZE    A number expressing the [RFC-822] size of the
                     message.

      RFC822.TEXT    Equivalent to BODY[TEXT].



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      UID            A number expressing the unique identifier of the
                     message.


   Example:    S: * 23 FETCH (FLAGS (\Seen) RFC822.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 AUTHORIZATION 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 expects it.  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



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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"
      RFC822.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" "INFOODS.MIT.EDU")) NIL NIL
      "<B27397-0100000@cac.washington.edu>")
       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] {350}
S:    Date: Wed, 17 Jul 1996 02:23:25 -0700 (PDT)
S:    From: Terry Gray <gray@cac.washington.edu>
S:    Subject: IMAP4rev1 WG mtg summary and minutes
S:    To: imap@cac.washington.edu
S:    cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@INFOODS.MIT.EDU>
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 (BNF) notation as specified in [RFC-822] with one exception; the
   delimiter used with the "#" construct is a single space (SPACE) and
   not one or more commas.

   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" could be
   parsed as a flag_extension.  Some, but not all, instances of this
   rule are noted below.




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   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.

address         ::= "(" addr_name SPACE addr_adl SPACE addr_mailbox
                    SPACE addr_host ")"

addr_adl        ::= nstring
                    ;; Holds route from [RFC-822] route-addr if
                    ;; non-NIL

addr_host       ::= nstring
                    ;; NIL indicates [RFC-822] group syntax.
                    ;; Otherwise, holds [RFC-822] domain name

addr_mailbox    ::= nstring
                    ;; NIL indicates end of [RFC-822] group; if
                    ;; non-NIL and addr_host is NIL, holds
                    ;; [RFC-822] group name.
                    ;; Otherwise, holds [RFC-822] local-part

addr_name       ::= nstring
                    ;; Holds phrase from [RFC-822] mailbox if
                    ;; non-NIL

alpha           ::= "A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" /
                    "I" / "J" / "K" / "L" / "M" / "N" / "O" / "P" /
                    "Q" / "R" / "S" / "T" / "U" / "V" / "W" / "X" /
                    "Y" / "Z" /
                    "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" /
                    "i" / "j" / "k" / "l" / "m" / "n" / "o" / "p" /
                    "q" / "r" / "s" / "t" / "u" / "v" / "w" / "x" /
                    "y" / "z"
                    ;; Case-sensitive

append          ::= "APPEND" SPACE mailbox [SPACE flag_list]
                    [SPACE date_time] SPACE literal

astring         ::= atom / string

atom            ::= 1*ATOM_CHAR

ATOM_CHAR       ::= <any CHAR except atom_specials>

atom_specials   ::= "(" / ")" / "{" / SPACE / CTL / list_wildcards /
                    quoted_specials




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authenticate    ::= "AUTHENTICATE" SPACE auth_type *(CRLF base64)

auth_type       ::= atom
                    ;; Defined by [IMAP-AUTH]

base64          ::= *(4base64_char) [base64_terminal]

base64_char     ::= alpha / digit / "+" / "/"

base64_terminal ::= (2base64_char "==") / (3base64_char "=")

body            ::= "(" body_type_1part / body_type_mpart ")"

body_extension  ::= nstring / number / "(" 1#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 [SPACE body_fld_dsp
                    [SPACE body_fld_lang
                    [SPACE 1#body_extension]]]
                    ;; MUST NOT be returned on non-extensible
                    ;; "BODY" fetch

body_ext_mpart  ::= body_fld_param
                    [SPACE body_fld_dsp SPACE body_fld_lang
                    [SPACE 1#body_extension]]
                    ;; MUST NOT be returned on non-extensible
                    ;; "BODY" fetch

body_fields     ::= body_fld_param SPACE body_fld_id SPACE
                    body_fld_desc SPACE body_fld_enc SPACE
                    body_fld_octets

body_fld_desc   ::= nstring

body_fld_dsp    ::= "(" string SPACE body_fld_param ")" / nil

body_fld_enc    ::= (<"> ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
                    "QUOTED-PRINTABLE") <">) / string

body_fld_id     ::= nstring

body_fld_lang   ::= nstring / "(" 1#string ")"




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body_fld_lines  ::= number

body_fld_md5    ::= nstring

body_fld_octets ::= number

body_fld_param  ::= "(" 1#(string SPACE string) ")" / nil

body_type_1part ::= (body_type_basic / body_type_msg / body_type_text)
                    [SPACE body_ext_1part]

body_type_basic ::= media_basic SPACE body_fields
                    ;; MESSAGE subtype MUST NOT be "RFC822"

body_type_mpart ::= 1*body SPACE media_subtype
                    [SPACE body_ext_mpart]

body_type_msg   ::= media_message SPACE body_fields SPACE envelope
                    SPACE body SPACE body_fld_lines

body_type_text  ::= media_text SPACE body_fields SPACE 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" SPACE [1#capability SPACE] "IMAP4rev1"
                    [SPACE 1#capability]
                    ;; IMAP4rev1 servers which offer RFC 1730
                    ;; compatibility MUST list "IMAP4" as the first
                    ;; capability.

CHAR            ::= <any 7-bit US-ASCII character except NUL,
                     0x01 - 0x7f>

CHAR8           ::= <any 8-bit octet except NUL, 0x01 - 0xff>

command         ::= tag SPACE (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



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command_nonauth ::= login / authenticate
                    ;; Valid only when in Non-Authenticated state

command_select  ::= "CHECK" / "CLOSE" / "EXPUNGE" /
                     copy / fetch / store / uid / search
                    ;; Valid only when in Selected state

continue_req    ::= "+" SPACE (resp_text / base64)

copy            ::= "COPY" SPACE set SPACE mailbox

CR              ::= <ASCII CR, carriage return, 0x0D>

create          ::= "CREATE" SPACE mailbox
                    ;; Use of INBOX gives a NO error

CRLF            ::= CR LF

CTL             ::= <any ASCII control character and DEL,
                        0x00 - 0x1f, 0x7f>

date            ::= date_text / <"> date_text <">

date_day        ::= 1*2digit
                    ;; Day of month

date_day_fixed  ::= (SPACE 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       ::= <"> date_day_fixed "-" date_month "-" date_year
                    SPACE time SPACE zone <">

delete          ::= "DELETE" SPACE mailbox
                    ;; Use of INBOX gives a NO error

digit           ::= "0" / digit_nz

digit_nz        ::= "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" /
                    "9"





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envelope        ::= "(" env_date SPACE env_subject SPACE env_from
                    SPACE env_sender SPACE env_reply_to SPACE env_to
                    SPACE env_cc SPACE env_bcc SPACE env_in_reply_to
                    SPACE 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" SPACE mailbox

fetch           ::= "FETCH" SPACE set SPACE ("ALL" / "FULL" /
                    "FAST" / fetch_att / "(" 1#fetch_att ")")

fetch_att       ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
                    "RFC822" [".HEADER" / ".SIZE" / ".TEXT"] /
                    "BODY" ["STRUCTURE"] / "UID" /
                    "BODY" [".PEEK"] section
                    ["<" number "." nz_number ">"]

flag            ::= "\Answered" / "\Flagged" / "\Deleted" /
                    "\Seen" / "\Draft" / flag_keyword / flag_extension

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_keyword    ::= atom



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flag_list       ::= "(" #flag ")"

greeting        ::= "*" SPACE (resp_cond_auth / resp_cond_bye) CRLF

header_fld_name ::= astring

header_list     ::= "(" 1#header_fld_name ")"

LF              ::= <ASCII LF, line feed, 0x0A>

list            ::= "LIST" SPACE mailbox SPACE list_mailbox

list_mailbox    ::= 1*(ATOM_CHAR / list_wildcards) / string

list_wildcards  ::= "%" / "*"

literal         ::= "{" number "}" CRLF *CHAR8
                    ;; Number represents the number of CHAR8 octets

login           ::= "LOGIN" SPACE userid SPACE password

lsub            ::= "LSUB" SPACE mailbox SPACE 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.  Refer to section 5.1 for
                    ;; further semantic details of mailbox names.

mailbox_data    ::=  "FLAGS" SPACE flag_list /
                     "LIST" SPACE mailbox_list /
                     "LSUB" SPACE mailbox_list /
                     "MAILBOX" SPACE text /
                     "SEARCH" [SPACE 1#nz_number] /
                     "STATUS" SPACE mailbox SPACE
                     "(" #<status_att number ")" /
                     number SPACE "EXISTS" / number SPACE "RECENT"

mailbox_list    ::= "(" #("\Marked" / "\Noinferiors" /
                    "\Noselect" / "\Unmarked" / flag_extension) ")"
                    SPACE (<"> QUOTED_CHAR <"> / nil) SPACE mailbox

media_basic     ::= (<"> ("APPLICATION" / "AUDIO" / "IMAGE" /
                    "MESSAGE" / "VIDEO") <">) / string)
                    SPACE media_subtype
                    ;; Defined in [MIME-IMT]

media_message   ::= <"> "MESSAGE" <"> SPACE <"> "RFC822" <">



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                    ;; Defined in [MIME-IMT]

media_subtype   ::= string
                    ;; Defined in [MIME-IMT]

media_text      ::= <"> "TEXT" <"> SPACE media_subtype
                    ;; Defined in [MIME-IMT]

message_data    ::= nz_number SPACE ("EXPUNGE" /
                                    ("FETCH" SPACE msg_att))

msg_att         ::= "(" 1#("ENVELOPE" SPACE envelope /
                    "FLAGS" SPACE "(" #(flag / "\Recent") ")" /
                    "INTERNALDATE" SPACE date_time /
                    "RFC822" [".HEADER" / ".TEXT"] SPACE nstring /
                    "RFC822.SIZE" SPACE number /
                    "BODY" ["STRUCTURE"] SPACE body /
                    "BODY" section ["<" number ">"] SPACE nstring /
                    "UID" SPACE uniqueid) ")"

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          ::= <"> *QUOTED_CHAR <">

QUOTED_CHAR     ::= <any TEXT_CHAR except quoted_specials> /
                    "\" quoted_specials

quoted_specials ::= <"> / "\"

rename          ::= "RENAME" SPACE mailbox SPACE mailbox
                    ;; Use of INBOX as a destination gives a NO error

response        ::= *(continue_req / response_data) response_done

response_data   ::= "*" SPACE (resp_cond_state / resp_cond_bye /
                    mailbox_data / message_data / capability_data)



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                    CRLF

response_done   ::= response_tagged / response_fatal

response_fatal  ::= "*" SPACE resp_cond_bye CRLF
                    ;; Server closes connection immediately

response_tagged ::= tag SPACE resp_cond_state CRLF

resp_cond_auth  ::= ("OK" / "PREAUTH") SPACE resp_text
                    ;; Authentication condition

resp_cond_bye   ::= "BYE" SPACE resp_text

resp_cond_state ::= ("OK" / "NO" / "BAD") SPACE resp_text
                    ;; Status condition

resp_text       ::= ["[" resp_text_code "]" SPACE] (text_mime2 / text)
                    ;; text SHOULD NOT begin with "[" or "="

resp_text_code  ::= "ALERT" / "PARSE" /
                    "PERMANENTFLAGS" SPACE "(" #(flag / "\*") ")" /
                    "READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
                    "UIDVALIDITY" SPACE nz_number /
                    "UNSEEN" SPACE nz_number /
                    atom [SPACE 1*<any TEXT_CHAR except "]">]

search          ::= "SEARCH" SPACE ["CHARSET" SPACE astring SPACE]
                    1#search_key
                    ;; [CHARSET] MUST be registered with IANA

search_key      ::= "ALL" / "ANSWERED" / "BCC" SPACE astring /
                    "BEFORE" SPACE date / "BODY" SPACE astring /
                    "CC" SPACE astring / "DELETED" / "FLAGGED" /
                    "FROM" SPACE astring /
                    "KEYWORD" SPACE flag_keyword / "NEW" / "OLD" /
                    "ON" SPACE date / "RECENT" / "SEEN" /
                    "SINCE" SPACE date / "SUBJECT" SPACE astring /
                    "TEXT" SPACE astring / "TO" SPACE astring /
                    "UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
                    "UNKEYWORD" SPACE flag_keyword / "UNSEEN" /
                    ;; Above this line were in [IMAP2]
                    "DRAFT" /
                    "HEADER" SPACE header_fld_name SPACE astring /
                    "LARGER" SPACE number / "NOT" SPACE search_key /
                    "OR" SPACE search_key SPACE search_key /
                    "SENTBEFORE" SPACE date / "SENTON" SPACE date /
                    "SENTSINCE" SPACE date / "SMALLER" SPACE number /



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                    "UID" SPACE set / "UNDRAFT" / set /
                    "(" 1#search_key ")"

section         ::= "[" [section_text / (nz_number *["." nz_number]
                    ["." (section_text / "MIME")])] "]"

section_text    ::= "HEADER" / "HEADER.FIELDS" [".NOT"]
                    SPACE header_list / "TEXT"

select          ::= "SELECT" SPACE mailbox

sequence_num    ::= nz_number / "*"
                    ;; * is the largest number in use.  For message
                    ;; sequence numbers, it is the number of messages
                    ;; in the mailbox.  For unique identifiers, it is
                    ;; the unique identifier of the last message in
                    ;; the mailbox.

set             ::= sequence_num / (sequence_num ":" sequence_num) /
                    (set "," set)
                    ;; Identifies a set of messages.  For message
                    ;; sequence numbers, these are consecutive
                    ;; numbers from 1 to the number of messages in
                    ;; the mailbox
                    ;; Comma delimits individual numbers, colon
                    ;; delimits between two numbers inclusive.
                    ;; Example: 2,4:7,9,12:* is 2,4,5,6,7,9,12,13,
                    ;; 14,15 for a mailbox with 15 messages.

SPACE           ::= <ASCII SP, space, 0x20>

status          ::= "STATUS" SPACE mailbox SPACE "(" 1#status_att ")"

status_att      ::= "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" /
                    "UNSEEN"

store           ::= "STORE" SPACE set SPACE store_att_flags

store_att_flags ::= (["+" / "-"] "FLAGS" [".SILENT"]) SPACE
                    (flag_list / #flag)

string          ::= quoted / literal

subscribe       ::= "SUBSCRIBE" SPACE mailbox

tag             ::= 1*<any ATOM_CHAR except "+">

text            ::= 1*TEXT_CHAR



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text_mime2       ::= "=?" <charset> "?" <encoding> "?"
                     <encoded-text> "?="
                     ;; Syntax defined in [MIME-HDRS]

TEXT_CHAR       ::= <any CHAR except CR and LF>

time            ::= 2digit ":" 2digit ":" 2digit
                    ;; Hours minutes seconds

uid             ::= "UID" SPACE (copy / fetch / search / store)
                    ;; Unique identifiers used instead of message
                    ;; sequence numbers

uniqueid        ::= nz_number
                    ;; Strictly ascending

unsubscribe     ::= "UNSUBSCRIBE" SPACE mailbox

userid          ::= astring

x_command       ::= "X" atom <experimental command arguments>

zone            ::= ("+" / "-") 4digit
                    ;; Signed four-digit value of hhmm representing
                    ;; hours and minutes west 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: RFC 1730,
   unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.

11.     Security Considerations

   IMAP4rev1 protocol transactions, including electronic mail data, are
   sent in the clear over the network unless privacy protection is
   negotiated in the AUTHENTICATE command.

   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 instead.



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   A server error message for a failing LOGIN command SHOULD NOT specify
   that the user name, as opposed to the password, is invalid.

   Additional security considerations are discussed in the section
   discussing the AUTHENTICATE and LOGIN commands.

12.     Author's Address

   Mark R. Crispin
   Networks and Distributed Computing
   University of Washington
   4545 15th Aveneue NE
   Seattle, WA  98105-4527

   Phone: (206) 543-5762

   EMail: MRC@CAC.Washington.EDU


































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Appendices

A.      References

[ACAP] Myers, J. "ACAP -- Application Configuration Access Protocol",
Work in Progress.

[CHARSET] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
RFC 1700, USC/Information Sciences Institute, October 1994.

[DISPOSITION] Troost, R., and Dorner, S., "Communicating Presentation
Information in Internet Messages: The Content-Disposition Header",
RFC 1806, June 1995.

[IMAP-AUTH] Myers, J., "IMAP4 Authentication Mechanism", RFC 1731.
Carnegie-Mellon University, December 1994.

[IMAP-COMPAT] Crispin, M., "IMAP4 Compatibility with IMAP2bis", RFC
2061, University of Washington, November 1996.

[IMAP-DISC] Austein, R., "Synchronization Operations for Disconnected
IMAP4 Clients", Work in Progress.

[IMAP-HISTORICAL] Crispin, M. "IMAP4 Compatibility with IMAP2 and
IMAP2bis", RFC 1732, University of Washington, December 1994.

[IMAP-MODEL] Crispin, M., "Distributed Electronic Mail Models in
IMAP4", RFC 1733, University of Washington, December 1994.

[IMAP-OBSOLETE] Crispin, M., "Internet Message Access Protocol -
Obsolete Syntax", RFC 2062, University of Washington, November 1996.

[IMAP2] Crispin, M., "Interactive Mail Access Protocol - Version 2",
RFC 1176, University of Washington, August 1990.

[LANGUAGE-TAGS] Alvestrand, H., "Tags for the Identification of
Languages", RFC 1766, March 1995.

[MD5] Myers, J., and M. Rose, "The Content-MD5 Header Field", RFC
1864, October 1995.

[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", RFC 2046,
November 1996.



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[MIME-HDRS] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996.

[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, University of Delaware, August 1982.

[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, USC/Information Sciences Institute, August 1982.

[UTF-7] Goldsmith, D., and Davis, M., "UTF-7: A Mail-Safe
Transformation Format of Unicode", RFC 1642, July 1994.

B.      Changes from RFC 1730

1) The STATUS command has been added.

2) Clarify in the formal syntax that the "#" construct can never
refer to multiple spaces.

3) Obsolete syntax has been moved to a separate document.

4) The PARTIAL command has been obsoleted.

5) The RFC822.HEADER.LINES, RFC822.HEADER.LINES.NOT, RFC822.PEEK, and
RFC822.TEXT.PEEK fetch attributes have been obsoleted.

6) The "<" origin "." size ">" suffix for BODY text attributes has
been added.

7) The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, MIME, and TEXT part
specifiers have been added.

8) Support for Content-Disposition and Content-Language has been
added.

9) The restriction on fetching nested MULTIPART parts has been
removed.

10) Body part number 0 has been obsoleted.

11) Server-supported authenticators are now identified by
capabilities.








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12) The capability that identifies this protocol is now called
"IMAP4rev1".  A server that provides backwards support for RFC 1730
SHOULD emit the "IMAP4" capability in addition to "IMAP4rev1" in its
CAPABILITY response.  Because RFC-1730 required "IMAP4" to appear as
the first capability, it MUST listed first in the response.

13) A description of the mailbox name namespace convention has been
added.

14) A description of the international mailbox name convention has
been added.

15) The UID-NEXT and UID-VALIDITY status items are now called UIDNEXT
and UIDVALIDITY.  This is a change from the IMAP STATUS
Work in Progress and not from RFC-1730

16) Add a clarification that a null mailbox name argument to the LIST
command returns an untagged LIST response with the hierarchy
delimiter and root of the reference argument.

17) Define terms such as "MUST", "SHOULD", and "MUST NOT".

18) Add a section which defines message attributes and more
thoroughly details the semantics of message sequence numbers, UIDs,
and flags.

19) Add a clarification detailing the circumstances when a client may
send multiple commands without waiting for a response, and the
circumstances in which ambiguities may result.

20) Add a recommendation on server behavior for DELETE and RENAME
when inferior hierarchical names of the given name exist.

21) Add a clarification that a mailbox name may not be unilaterally
unsubscribed by the server, even if that mailbox name no longer
exists.

22) Add a clarification that LIST should return its results quickly
without undue delay.

23) Add a clarification that the date_time argument to APPEND sets
the internal date of the message.

24) Add a clarification on APPEND behavior when the target mailbox is
the currently selected mailbox.






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25) Add a clarification that external changes to flags should be
always announced via an untagged FETCH even if the current command is
a STORE with the ".SILENT" suffix.

26) Add a clarification that COPY appends to the target mailbox.

27) Add the NEWNAME response code.

28) Rewrite the description of the untagged BYE response to clarify
its semantics.

29) Change the reference for the body MD5 to refer to the proper RFC.

30) Clarify that the formal syntax contains rules which may overlap,
and that in the event of such an overlap the rule which occurs first
takes precedence.

31) Correct the definition of body_fld_param.

32) More formal syntax for capability_data.

33) Clarify that any case variant of "INBOX" must be interpreted as
INBOX.

34) Clarify that the human-readable text in resp_text should not
begin with "[" or "=".

35) Change MIME references to Draft Standard documents.

36) Clarify \Recent semantics.

37) Additional examples.

C.      Key Word Index

       +FLAGS <flag list> (store command data item) ...............   45
       +FLAGS.SILENT <flag list> (store command data item) ........   46
       -FLAGS <flag list> (store command data item) ...............   46
       -FLAGS.SILENT <flag list> (store command data item) ........   46
       ALERT (response code) ......................................   50
       ALL (fetch item) ...........................................   41
       ALL (search key) ...........................................   38
       ANSWERED (search key) ......................................   38
       APPEND (command) ...........................................   34
       AUTHENTICATE (command) .....................................   20
       BAD (response) .............................................   52
       BCC <string> (search key) ..................................   38
       BEFORE <date> (search key) .................................   39



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       BODY (fetch item) ..........................................   41
       BODY (fetch result) ........................................   58
       BODY <string> (search key) .................................   39
       BODY.PEEK[<section>]<<partial>> (fetch item) ...............   44
       BODYSTRUCTURE (fetch item) .................................   44
       BODYSTRUCTURE (fetch result) ...............................   59
       BODY[<section>]<<origin_octet>> (fetch result) .............   58
       BODY[<section>]<<partial>> (fetch item) ....................   41
       BYE (response) .............................................   52
       Body Structure (message attribute) .........................   11
       CAPABILITY (command) .......................................   18
       CAPABILITY (response) ......................................   53
       CC <string> (search key) ...................................   39
       CHECK (command) ............................................   36
       CLOSE (command) ............................................   36
       COPY (command) .............................................   46
       CREATE (command) ...........................................   25
       DELETE (command) ...........................................   26
       DELETED (search key) .......................................   39
       DRAFT (search key) .........................................   39
       ENVELOPE (fetch item) ......................................   44
       ENVELOPE (fetch result) ....................................   62
       EXAMINE (command) ..........................................   24
       EXISTS (response) ..........................................   56
       EXPUNGE (command) ..........................................   37
       EXPUNGE (response) .........................................   57
       Envelope Structure (message attribute) .....................   11
       FAST (fetch item) ..........................................   44
       FETCH (command) ............................................   41
       FETCH (response) ...........................................   58
       FLAGGED (search key) .......................................   39
       FLAGS (fetch item) .........................................   44
       FLAGS (fetch result) .......................................   62
       FLAGS (response) ...........................................   56
       FLAGS <flag list> (store command data item) ................   45
       FLAGS.SILENT <flag list> (store command data item) .........   45
       FROM <string> (search key) .................................   39
       FULL (fetch item) ..........................................   44
       Flags (message attribute) ..................................    9
       HEADER (part specifier) ....................................   41
       HEADER <field-name> <string> (search key) ..................   39
       HEADER.FIELDS <header_list> (part specifier) ...............   41
       HEADER.FIELDS.NOT <header_list> (part specifier) ...........   41
       INTERNALDATE (fetch item) ..................................   44
       INTERNALDATE (fetch result) ................................   62
       Internal Date (message attribute) ..........................   10
       KEYWORD <flag> (search key) ................................   39
       Keyword (type of flag) .....................................   10



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       LARGER <n> (search key) ....................................   39
       LIST (command) .............................................   30
       LIST (response) ............................................   54
       LOGIN (command) ............................................   22
       LOGOUT (command) ...........................................   20
       LSUB (command) .............................................   32
       LSUB (response) ............................................   55
       MAY (specification requirement term) .......................    5
       MESSAGES (status item) .....................................   33
       MIME (part specifier) ......................................   42
       MUST (specification requirement term) ......................    4
       MUST NOT (specification requirement term) ..................    4
       Message Sequence Number (message attribute) ................    9
       NEW (search key) ...........................................   39
       NEWNAME (response code) ....................................   50
       NO (response) ..............................................   51
       NOOP (command) .............................................   19
       NOT <search-key> (search key) ..............................   39
       OK (response) ..............................................   51
       OLD (search key) ...........................................   39
       ON <date> (search key) .....................................   39
       OPTIONAL (specification requirement term) ..................    5
       OR <search-key1> <search-key2> (search key) ................   39
       PARSE (response code) ......................................   50
       PERMANENTFLAGS (response code) .............................   50
       PREAUTH (response) .........................................   52
       Permanent Flag (class of flag) .............................   10
       READ-ONLY (response code) ..................................   50
       READ-WRITE (response code) .................................   50
       RECENT (response) ..........................................   57
       RECENT (search key) ........................................   39
       RECENT (status item) .......................................   33
       RENAME (command) ...........................................   27
       REQUIRED (specification requirement term) ..................    4
       RFC822 (fetch item) ........................................   44
       RFC822 (fetch result) ......................................   63
       RFC822.HEADER (fetch item) .................................   44
       RFC822.HEADER (fetch result) ...............................   62
       RFC822.SIZE (fetch item) ...................................   44
       RFC822.SIZE (fetch result) .................................   62
       RFC822.TEXT (fetch item) ...................................   44
       RFC822.TEXT (fetch result) .................................   62
       SEARCH (command) ...........................................   37
       SEARCH (response) ..........................................   55
       SEEN (search key) ..........................................   40
       SELECT (command) ...........................................   23
       SENTBEFORE <date> (search key) .............................   40
       SENTON <date> (search key) .................................   40



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       SENTSINCE <date> (search key) ..............................   40
       SHOULD (specification requirement term) ....................    5
       SHOULD NOT (specification requirement term) ................    5
       SINCE <date> (search key) ..................................   40
       SMALLER <n> (search key) ...................................   40
       STATUS (command) ...........................................   33
       STATUS (response) ..........................................   55
       STORE (command) ............................................   45
       SUBJECT <string> (search key) ..............................   40
       SUBSCRIBE (command) ........................................   29
       Session Flag (class of flag) ...............................   10
       System Flag (type of flag) .................................    9
       TEXT (part specifier) ......................................   42
       TEXT <string> (search key) .................................   40
       TO <string> (search key) ...................................   40
       TRYCREATE (response code) ..................................   51
       UID (command) ..............................................   47
       UID (fetch item) ...........................................   44
       UID (fetch result) .........................................   63
       UID <message set> (search key) .............................   40
       UIDNEXT (status item) ......................................   33
       UIDVALIDITY (response code) ................................   51
       UIDVALIDITY (status item) ..................................   34
       UNANSWERED (search key) ....................................   40
       UNDELETED (search key) .....................................   40
       UNDRAFT (search key) .......................................   40
       UNFLAGGED (search key) .....................................   40
       UNKEYWORD <flag> (search key) ..............................   40
       UNSEEN (response code) .....................................   51
       UNSEEN (search key) ........................................   40
       UNSEEN (status item) .......................................   34
       UNSUBSCRIBE (command) ......................................   30
       Unique Identifier (UID) (message attribute) ................    7
       X<atom> (command) ..........................................   48
       [RFC-822] Size (message attribute) .........................   11
       \Answered (system flag) ....................................    9
       \Deleted (system flag) .....................................    9
       \Draft (system flag) .......................................    9
       \Flagged (system flag) .....................................    9
       \Marked (mailbox name attribute) ...........................   54
       \Noinferiors (mailbox name attribute) ......................   54
       \Noselect (mailbox name attribute) .........................   54
       \Recent (system flag) ......................................   10
       \Seen (system flag) ........................................    9
       \Unmarked (mailbox name attribute) .........................   54






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