path: root/doc/rfc/rfc1730.txt

Network Working Group                                         M. Crispin
Request for Comments: 1730                      University of Washington
Category: Standards Track                                  December 1994


              INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4



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 4 (IMAP4) allows a
   client to access and manipulate electronic mail messages on a server.
   IMAP4 permits manipulation of remote message folders, called
   "mailboxes", in a way that is functionally equivalent to local
   mailboxes.  IMAP4 also provides the capability for an offline client
   to resynchronize with the server (see also [IMAP-DISC]).

   IMAP4 includes operations for creating, deleting, and renaming
   mailboxes; checking for new messages; permanently removing messages;
   setting and clearing flags; RFC 822 and MIME parsing; searching; and
   selective fetching of message attributes, texts, and portions
   thereof.  Messages in IMAP4 are accessed by the use of numbers.
   These numbers are either message sequence numbers (relative position
   from 1 to the number of messages in the mailbox) or unique
   identifiers (immutable, strictly ascending values assigned to each
   message, but which are not necessarily contiguous).

   IMAP4 supports a single server.  A mechanism for supporting multiple
   IMAP4 servers is discussed in [IMSP].

   IMAP4 does not specify a means of posting mail; this function is
   handled by a mail transfer protocol such as [SMTP].

   IMAP4 is designed to be upwards compatible from the [IMAP2] protocol.
   Compatibility issues are discussed in [IMAP-COMPAT].






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Table of Contents



IMAP4 Protocol Specification ......................................    1
1.      Organization of this Document .............................    1
1.1.    How to Read This Document .................................    1
1.2.    Conventions Used in this Document .........................    1
2.      Protocol Overview .........................................    1
2.1.    Link Level ................................................    1
2.2.    Commands and Responses ....................................    1
2.2.1.  Client Protocol Sender and Server Protocol Receiver .......    2
2.2.2.  Server Protocol Sender and Client Protocol Receiver .......    2
3.      State and Flow Diagram ....................................    4
3.1.    Non-Authenticated State ...................................    4
3.2.    Authenticated State .......................................    4
3.3.    Selected State ............................................    4
3.4.    Logout State ..............................................    4
4.      Data Formats ..............................................    6
4.1.    Atom ......................................................    6
4.2.    Number ....................................................    6
4.3.    String ....................................................    6
4.3.1.  8-bit and Binary Strings ..................................    7
4.4.    Parenthesized List ........................................    7
4.5.    NIL .......................................................    7
5.      Operational Considerations ................................    8
5.1.    Mailbox Naming ............................................    8
5.2.    Mailbox Size and Message Status Updates ...................    8
5.3.    Response when no Command in Progress ......................    8
5.4.    Autologout Timer ..........................................    9
5.5.    Multiple Commands in Progress .............................    9
6.      Client Commands ...........................................   10
6.1.    Client Commands - Any State ...............................   10
6.1.1.  CAPABILITY Command ........................................   10
6.1.2.  NOOP Command ..............................................   11
6.1.3.  LOGOUT Command ............................................   11
6.2.    Client Commands - Non-Authenticated State .................   12
6.2.1.  AUTHENTICATE Command ......................................   12
6.2.2.  LOGIN Command .............................................   14
6.3.    Client Commands - Authenticated State .....................   14
6.3.1.  SELECT Command ............................................   15
6.3.2.  EXAMINE Command ...........................................   16
6.3.3.  CREATE Command ............................................   17
6.3.4.  DELETE Command ............................................   18
6.3.5.  RENAME Command ............................................   18



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6.3.6.  SUBSCRIBE Command .........................................   19
6.3.7.  UNSUBSCRIBE Command .......................................   19
6.3.8.  LIST Command ..............................................   20
6.3.9.  LSUB Command ..............................................   22
6.3.10. APPEND Command ............................................   22
6.4.    Client Commands - Selected State ..........................   23
6.4.1.  CHECK Command .............................................   23
6.4.2.  CLOSE Command .............................................   24
6.4.3.  EXPUNGE Command ...........................................   25
6.4.4.  SEARCH Command ............................................   25
6.4.5.  FETCH Command .............................................   29
6.4.6.  PARTIAL Command ...........................................   32
6.4.7.  STORE Command .............................................   33
6.4.8.  COPY Command ..............................................   34
6.4.9.  UID Command ...............................................   35
6.5.    Client Commands - Experimental/Expansion ..................   37
6.5.1.  X<atom> Command ...........................................   37
7.      Server Responses ..........................................   38
7.1.    Server Responses - Status Responses .......................   39
7.1.1.  OK Response ...............................................   40
7.1.2.  NO Response ...............................................   40
7.1.3.  BAD Response ..............................................   41
7.1.4.  PREAUTH Response ..........................................   41
7.1.5.  BYE Response ..............................................   41
7.2.    Server Responses - Server and Mailbox Status ..............   42
7.2.1.  CAPABILITY Response .......................................   42
7.2.2.  LIST Response .............................................   43
7.2.3.  LSUB Response .............................................   44
7.2.4.  SEARCH Response ...........................................   44
7.2.5.  FLAGS Response ............................................   44
7.3.    Server Responses - Message Status .........................   45
7.3.1.  EXISTS Response ...........................................   45
7.3.2.  RECENT Response ...........................................   45
7.3.3.  EXPUNGE Response ..........................................   45
7.3.4.  FETCH Response ............................................   46
7.3.5.  Obsolete Responses ........................................   51
7.4.    Server Responses - Command Continuation Request ...........   51
8.      Sample IMAP4 session ......................................   52
9.      Formal Syntax .............................................   53
10.     Author's Note .............................................   64
11.     Security Considerations ...................................   64
12.     Author's Address ..........................................   64
Appendices ........................................................   65
A.      Obsolete Commands .........................................   65
A.6.3.OBS.1.    FIND ALL.MAILBOXES Command ........................   65
A.6.3.OBS.2.    FIND MAILBOXES Command ............................   65
A.6.3.OBS.3.    SUBSCRIBE MAILBOX Command .........................   66
A.6.3.OBS.4.    UNSUBSCRIBE MAILBOX Command .......................   66



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B.      Obsolete Responses ........................................   68
B.7.2.OBS.1.    MAILBOX Response ..................................   68
B.7.3.OBS.1.    COPY Response .....................................   68
B.7.3.OBS.2.    STORE Response ....................................   69
C.      References ................................................   70
E.      IMAP4 Keyword Index .......................................   71













































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IMAP4 Protocol Specification

1.      Organization of this Document

1.1.    How to Read This Document

   This document is written from the point of view of the implementor of
   an IMAP4 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 IMAP4 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, one should not attempt to deduce command syntax from the
   command section alone; one should 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.


2.      Protocol Overview

2.1.    Link Level

   The IMAP4 protocol assumes a reliable data stream such as provided by
   TCP.  When TCP is used, an IMAP4 server listens on port 143.


2.2.    Commands and Responses

   An IMAP4 session consists of the establishment of a client/server
   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 IMAP4 client or server is either reading a line, or is reading
   a sequence of octets with a known count followed by a line.






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2.2.1.  Client Protocol Sender and Server Protocol Receiver

   The client command begins an operation.  Each client command is
   prefixed with a 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.

   The protocol receiver of an IMAP4 server reads a command line from
   the client, parses the command and its arguments, and transmits
   server data and a server command completion result response.


2.2.2.  Server Protocol Sender and Client Protocol Receiver

   Data transmitted by the server to the client and status responses
   that do not indicate command completion are prefixed with the token
   "*", and are called untagged responses.

   Server data may be sent as a result of a client command, or may be
   sent unilaterally by the server.  There is no syntactic difference
   between server data that resulted from a specific command and server
   data that were sent unilaterally.

   The server completion result response indicates the success or
   failure of the operation.  It is tagged with the same tag as the
   client command which began the operation.  Thus, if more than one



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   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 IMAP4 client reads a response line from
   the server.  It then takes action on the response based upon the
   first token of the response, which may be a tag, a "*", or a "+".  As
   described above.

   A client MUST be prepared to accept any server response at all times.
   This includes server data that it may not have 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, recording the data is
   mandatory.

   This topic is discussed in greater detail in the Server Responses
   section.































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3.      State and Flow Diagram

   An IMAP4 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 user 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 user 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.


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 session 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.














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            +--------------------------------------+
            |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




















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4.      Data Formats

   IMAP4 uses textual commands and responses.  Data in IMAP4 can be in
   one of several forms: atom, number, string, parenthesized list, or
   NIL.


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 restrictions of what may be 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 respresented 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.







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4.3.1.  8-bit and Binary Strings

   8-bit textual and binary mail is supported through the use of
   [MIME-1] encoding.  IMAP4 implementations MAY transmit 8-bit or
   multi-octet characters in literals, but should do so only when the
   character set is identified.

   Although a BINARY body encoding is defined, unencoded binary strings
   are not permitted.  A "binary string" is any string with NUL
   characters.  Implementations MUST encode binary data into a textual
   form such as BASE64 before transmitting the data.  A string with an
   excessive amount of CTL characters may also be considered to be
   binary, although this is not required.


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 may itself 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 ().



















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5.      Operational Considerations

5.1.    Mailbox Naming

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

5.2.    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 details.

   Regardless of what implementation decisions a client may take 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.










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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.


5.5.    Multiple Commands in Progress

   The client is not required to wait for the completion result response
   of a command before sending another command, subject to flow control
   constraints on the underlying data stream.  Similarly, a server is
   not required to process a command to completion before beginning
   processing of the next command, unless an ambiguity would result
   because of a command that would affect the results of other commands.
   If there is such an ambiguity, the server executes commands to
   completion in the order given by the client.

































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6.      Client Commands

   IMAP4 commands are described in this section.  Commands are organized
   by the state in which the command is permitted.  Commands which are
   permitted in multiple states are listed in the minimum permitted
   state (for example, commands valid in authenticated and selected
   state are listed in the authenticated state commands).

   Command arguments, identified by "Arguments:" in the command
   descriptions below, are described by function, not by syntax.  The
   precise syntax of command arguments is described in the Formal Syntax
   section.

   Some commands cause specific server data to be returned; these are
   identified by "Data:" 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 data 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

   Data:       mandatory 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 "IMAP4" as the first listed capability
      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
      session.



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      Capability names other than "IMAP4" refer to extensions,
      revisions, or amendments to this specification.  See the
      documentation of the CAPABILITY response for additional
      information.  No capabilities 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 IMAP4
               S: abcd OK CAPABILITY completed


6.1.2.  NOOP Command

   Arguments:  none

   Data:       no specific data 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

   Data:       mandatory 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 session.  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 IMAP4 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

   Data:       continuation data may 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
      user.  Optionally, it also negotiates a 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 should issue 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 protocol session.  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.

      The server is not required to support any particular
      authentication mechanism, nor are authentication mechanisms
      required to support any protection mechanisms.  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 IMAP4 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

   Data:       no specific data 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 user 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.







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   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,
   and APPEND.

6.3.1.  SELECT Command

   Arguments:  mailbox name

   Data:       mandatory 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

         <n> EXISTS  The number of messages in the mailbox

         <n> RECENT  The number of messages added to the  mailbox  since
                     the previous time this mailbox was read

         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.  If it
      is not possible to determine the messages that were added since
      the previous time a mailbox was read, then all messages SHOULD be
      considered recent.

      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 may change permanently.

      Only one mailbox may be selected at a time in a session;
      simultaneous access to multiple mailboxes requires multiple



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      sessions.  The SELECT command automatically deselects any
      currently selected mailbox before attempting the new selection.
      Consequently, if a mailbox is selected and a SELECT command that
      fails is attempted, no mailbox is selected.

      If the user 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 user 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 user's .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

   Data:       mandatory 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

   Data:       no specific data 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 may, in the
      future, create mailbox names under this name in the hierarchy.
      Server implementations that do not require this declaration MUST
      ignore it.

      If a new mailbox is created with the same name as a mailbox which
      was deleted, its unique identifiers MUST be greater than any
      unique identifiers used in the previous incarnation of the mailbox
      UNLESS the new incarnation has a different unique identifier
      validity value.  See the description of the UID command for more
      detail.

   Example:    C: A003 CREATE owatagusiam/
               S: A003 OK CREATE completed
               C: A004 CREATE owatagusiam/blurdybloop
               S: A004 OK CREATE completed




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        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

   Data:       no specific data 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.  Any error in deletion will
      return a tagged NO response.

      The value of the highest-used unique indentifier 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.

   Example:    C: A683 DELETE blurdybloop
               S: A683 OK DELETE completed


6.3.5.  RENAME Command

   Arguments:  existing mailbox name
               new mailbox name

   Data:       no specific data 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





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      The RENAME command changes the name of a mailbox.  A tagged OK
      response is returned only if the mailbox has been renamed.  It is
      an error to attempt to rename from a mailbox name that does not
      exist or to a mailbox name that already exists.  Any error in
      renaming will return a tagged NO response.

      Renaming INBOX is permitted; a new, empty INBOX is created in its
      place.

   Example:    C: Z4S9 RENAME blurdybloop owatagusiam
               S: Z4S9 OK RENAME completed


6.3.6.  SUBSCRIBE Command

   Arguments:  mailbox

   Data:       no specific data 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.

   Example:    C: A002 SUBSCRIBE #news.comp.mail.mime
               S: A002 OK SUBSCRIBE completed


6.3.7.  UNSUBSCRIBE Command

   Arguments:  mailbox name

   Data:       no specific data 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.





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   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

   Data:       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 user.  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.

      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.

      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.









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           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 detail).

      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 it
      matches the input arguments and INBOX is supported by this server
      for this user.  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: A002 LIST "~/Mail/" "%"
               S: * LIST (\Noselect) "/" ~/Mail/foo
               S: * LIST () "/" ~/Mail/meetings
               S: A002 OK LIST completed






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6.3.9.  LSUB Command

   Arguments:  reference name
               mailbox name with possible wildcards

   Data:       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.

   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. APPEND Command

   Arguments:  mailbox name
               optional flag parenthesized list
               optional date/time string
               message literal

   Data:       no specific data 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
      in the specified destination mailbox.  This argument is 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 [MIME-1] encoding.

      If a flag parenthesized list or date_time are specified, that data
      SHOULD be set in the resulting message; otherwise, the defaults of
      empty flags and the current date/time are used.





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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 mailbox is currently selected, the
      normal new mail actions should occur.

      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.

   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, FIND
   ALL.MAILBOXES, FIND MAILBOXES, and APPEND), the following commands
   are valid in the selected state: CHECK, CLOSE, EXPUNGE, SEARCH,
   FETCH, PARTIAL, STORE, COPY, and UID.








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6.4.1.  CHECK Command

   Arguments:  none

   Data:       no specific data 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

   Data:       no specific data 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 when a mailbox is selected, it is not required to send a
      CLOSE command before a SELECT, EXAMINE, or LOGOUT command.  The
      SELECT, EXAMINE, and LOGOUT commands implicitly close the
      currently selected mailbox without doing an expunge.  However,



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      when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT
      sequence is considerably faster than an EXPUNGE-LOGOUT or
      EXPUNGE-SELECT because no untagged EXPUNGE responses (which the
      client would probably ignore) are sent.

   Example:    C: A341 CLOSE
               S: A341 OK CLOSE completed


6.4.3.  EXPUNGE Command

   Arguments:  none

   Data:       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.
















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6.4.4.  SEARCH Command

   Arguments:  optional character set specification
               searching criteria (one or more)

   Data:       mandatory untagged response: SEARCH

   Result:     OK - search completed
               NO - search error: can't search that character set or
                    criteria
               BAD - command unknown or arguments invalid

      The SEARCH command searches the mailbox for messages that match
      the given searching criteria.  Searching criteria consist of one
      or more search keys.  The untagged SEARCH response from the server
      contains a listing of message sequence numbers corresponding to
      those messages that match the searching criteria.

      When multiple keys are specified, the result is the intersection
      (AND function) of all the messages that match those keys.  For
      example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers
      to all deleted messages from Smith that were placed in the mailbox
      since February 1, 1994.  A search key may 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-1] body parts with
      terminal content types other than TEXT and MESSAGE from
      consideration in SEARCH matching.

      The optional character set specification consists of the word
      "CHARSET" followed by a registered MIME character set.  It
      indicates the character set of the strings that appear in the
      search criteria.  [MIME-2] strings that appear in RFC 822/MIME
      message headers, and [MIME-1] content transfer encodings, MUST be
      decoded before matching.  Except for US-ASCII, it is not required
      that any particular character set be supported.  If the server
      does not support the specified character set, 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.








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      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.

      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 RFC822.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)".



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      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.

      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 RFC822.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.



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      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.


   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

   Data:       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 may 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>]
                     The text of a particular body section.  The section
                     specification is a set of one or more part numbers
                     delimited by periods.

                     Single-part messages only have a part 1.




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                     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.
                     It is not permitted to fetch a multipart part
                     itself, only its individual members.

                     A part of type MESSAGE and subtype RFC822 also has
                     nested parts.  These are the parts of the MESSAGE
                     part's body.  Nested part 0 of a part of type
                     MESSAGE and subtype RFC822 is the [RFC-822] header
                     of the message.

                     Every message has at least one part.

                          Here is an example of a complex message
                          with its associated section
                          specifications:

                           0   ([RFC-822] header of the message)
                               MULTIPART/MIXED
                           1   TEXT/PLAIN
                           2   APPLICATION/OCTET-STREAM
                           3   MESSAGE/RFC822
                           3.0   ([RFC-822] header of the message)
                           3.1   TEXT/PLAIN
                           3.2   APPLICATION/OCTET-STREAM
                                 MULTIPART/MIXED
                           4.1   IMAGE/GIF
                           4.2   MESSAGE/RFC822
                           4.2.0   ([RFC-822] header of the message)
                           4.2.1   TEXT/PLAIN
                                   MULTIPART/ALTERNATIVE
                           4.2.2.1  TEXT/PLAIN
                           4.2.2.2  TEXT/RICHTEXT

                          Note that there is no section
                          specification for the Multi-part parts
                          (no section 4 or 4.2.2).

                     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>]
                     An alternate form of BODY[section] that does not
                     implicitly set the \Seen flag.



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      BODYSTRUCTURE  The [MIME-1] body structure of the message.  This
                     is computed by the server by parsing the [MIME-1]
                     header lines.

      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 date and time of final delivery of the message
                     as defined by RFC 821.

      RFC822         The message in [RFC-822] format.  The \Seen flag is
                     implicitly set; if this causes the flags to change
                     they should be included as part of the fetch
                     responses.  This is the concatenation of
                     RFC822.HEADER and RFC822.TEXT.

      RFC822.PEEK    An alternate form of RFC822 that does not
                     implicitly set the \Seen flag.

      RFC822.HEADER  The [RFC-822] format header of the message as
                     stored on the server including the delimiting blank
                     line between the header and the body.

      RFC822.HEADER.LINES <header_list>
                     All header lines (including continuation lines) of
                     the [RFC-822] format header of the message with a
                     field-name (as defined in [RFC-822]) that matches
                     any of the strings in header_list.  The matching is
                     case-insensitive but otherwise exact.  The
                     delimiting blank line between the header and the
                     body is always included.










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      RFC822.HEADER.LINES.NOT <header_list>
                     All header lines (including continuation lines) of
                     the [RFC-822] format header of the message with a
                     field-name (as defined in [RFC-822]) that does not
                     match any of the strings in header_list.  The
                     matching is case-insensitive but otherwise exact.
                     The delimiting blank line between the header and
                     the body is always included.

      RFC822.SIZE    The number of octets in the message, as expressed
                     in [RFC-822] format.

      RFC822.TEXT    The text body of the message, omitting the
                     [RFC-822] header.  The \Seen flag is implicitly
                     set; if this causes the flags to change they should
                     be included as part of the fetch responses.

      RFC822.TEXT.PEEK
                     An alternate form of RFC822.TEXT that does not
                     implicitly set the \Seen flag.

      UID            The unique identifier for the message.


   Example:    C: A654 FETCH 2:4 (FLAGS RFC822.HEADER.LINES (DATE FROM))
               S: * 2 FETCH ....
               S: * 3 FETCH ....
               S: * 4 FETCH ....
               S: A003 OK FETCH completed


6.4.6.  PARTIAL Command

   Arguments:  message sequence number
               message data item name
               position of first octet
               number of octets

   Data:       untagged responses: FETCH

   Result:     OK - partial completed
               NO - partial error: can't fetch that data
               BAD - command unknown or arguments invalid

      The PARTIAL command is equivalent to the associated FETCH command,
      with the added functionality that only the specified number of
      octets, beginning at the specified starting octet, are returned.
      Only a single message can be fetched at a time.  The first octet



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      of a message, and hence the minimum for the starting octet, is
      octet 1.

      The following FETCH items are valid data for PARTIAL: RFC822,
      RFC822.HEADER, RFC822.TEXT, BODY[section], as well as any .PEEK
      forms of these.

      Any partial fetch that attempts to read beyond the end of the text
      is truncated as appropriate.  If the starting octet is beyond the
      end of the text, an empty string is returned.

      The data are returned with the FETCH response.  There is no
      indication of the range of the partial data in this response.  It
      is not possible to stream multiple PARTIAL commands of the same
      data item without processing and synchronizing at each step, since
      streamed commands may be executed out of order.

      There is no requirement that partial fetches follow any sequence.
      For example, if a partial fetch of octets 1 through 10000 breaks
      in an awkward place for BASE64 decoding, it is permitted to
      continue with a partial fetch of 9987 through 19987, etc.

      The handling of the \Seen flag is the same as in the associated
      FETCH command.

   Example:    C: A005 PARTIAL 4 RFC822 1 1024
               S: * 1 FETCH (RFC822 {1024}
               S: Return-Path: <gray@cac.washington.edu>
               S: ...
               S: .........  FLAGS (\Seen))
               S: A005 OK PARTIAL completed


6.4.7.  STORE Command

   Arguments:  message set
               message data item name
               value for message data item

   Data:       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



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      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.

      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.

      +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












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6.4.8.  COPY Command

   Arguments:  message set
               mailbox name

   Data:       no specific data 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 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.

      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


6.4.9.  UID Command

   Arguments:  command name
               command arguments

   Data:       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.



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      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.

      A unique identifier of a message is a number, and is guaranteed
      not to refer to any other message in the mailbox.  Unique
      identifiers are assigned in a strictly ascending fashion for each
      message added to the mailbox.  Unlike message sequence numbers,
      unique identifiers 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 message selection time.  If unique
      identifiers from an earlier session fail to persist to this
      session, the unique identifier validity value MUST be greater than
      in the earlier session.

           Note: An example of a good value to use for the unique
           identifier validity value would be 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 identifers will never be
           reused, even in the case of a mailbox being deleted and
           a new mailbox by the same name created at some future
           time.


      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 UID was specified
      as a message data item to the FETCH.





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   Example:    C: A003 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

   Data:       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, or a standard
      or standards-track revision of this specification, 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 IMAP4 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














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7.      Server Responses

   Server responses are in three forms: status responses, server data,
   and command continuation request.

   Server response data, identified by "Data:" in the response
   descriptions below, are described by function, not by syntax.  The
   precise syntax of server response data is described in the Formal
   Syntax section.

   The client MUST be prepared to accept any response at all times.

   Status responses that are tagged indicate the completion result 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 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 messags).

   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 responses occurs when the IMAP
   connection is in selected state.  In selected state, the server
   checks the mailbox for new messages as part of the execution of each
   command.  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.



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7.1.    Server Responses - Status Responses

   Status responses may include an optional response code.  A response
   code consists of data inside square brackets in the form of an atom,
   possibly followed by a space and arguments.  The response code
   contains additional information or status codes for client software
   beyond the OK/NO/BAD condition, and are defined when there is a
   specific action that a client can take based upon the additional
   information.

   The currently defined response codes are:

      ALERT          The human-readable text contains a special alert
                     that MUST be presented to the user in a fashion
                     that calls the user's attention to the message.

      PARSE          The human-readable text represents an error in
                     parsing the [RFC-822] or [MIME-1] headers of a
                     message in the mailbox.

      PERMANENTFLAGS Followed by a parenthesized list of flags,
                     indicates which of the known flags that the client
                     may 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 may also include the special
                     flag \*, which indicates that it is possible to
                     create new keywords by attempting to store those
                     flags in the mailbox.

      READ-ONLY      The mailbox is selected read-only, or its access
                     while selected has changed from read-write to
                     read-only.

      READ-WRITE     The mailbox is selected read-write, or its access
                     while selected has changed from read-only to
                     read-write.

      TRYCREATE      An APPEND or COPY attempt is failing because the
                     target mailbox does not exist (as opposed to some
                     other reason).  This is a hint to the client that
                     the operation may succeed if the mailbox is first
                     created by the CREATE command.




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      UIDVALIDITY    Followed by a decimal number, indicates the unique
                     identifier validity value.  See the description of
                     the UID command for more detail.

      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

   Data:       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 session startup.  It indicates that the session is not yet
      authenticated and that a LOGIN command is needed.

   Example:    S: * OK IMAP4 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

   Data:       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 may 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: A222 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: A222 NO COPY failed: disk is full


7.1.3.  BAD Response

   Data:       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 may 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

   Data:       optional response code
               human-readable text

      The PREAUTH response is always untagged, and is one of three
      possible greetings at session startup.  It indicates that the
      session has already been authenticated by external means and thus
      no LOGIN command is needed.

   Example:    S: * PREAUTH IMAP4 server ready and logged in as Smith









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7.1.5.  BYE Response

   Data:       optional response code
               human-readable text

      The BYE response is always untagged, and indicates that the server
      is about to close the connection.  The human-readable text may be
      displayed to the user in a status report by the client.  The BYE
      response may be sent as part of a normal logout sequence, or as a
      panic shutdown announcement by the server.  It is also used by
      some server implementations as an announcement of an inactivity
      autologout.

      This response is also used as one of three possible greetings at
      session startup.  It indicates that the server is not willing to
      accept a session from this client.

   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 data are
   transmitted from the server to the client, often as a result of a
   command with the same name.

7.2.1.  CAPABILITY Response

   Data:       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 first
      name in the capability listing MUST be the atom "IMAP4".

      A capability name other than IMAP4 indicates that the server
      supports an extension, revision, or amendment to the IMAP4
      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 IMAP4 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".





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      Client implementations SHOULD NOT require any capability name
      other than "IMAP4", and MUST ignore any unknown capability names.

   Example:    S: * CAPABILITY IMAP4 XPIG-LATIN


7.2.2.  LIST Response

   Data:       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
      may 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.

      The hierarchy delimiter is a character used to delimit levels of
      hierarchy in a mailbox name.  A client may 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.







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      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

   Data:       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
      may 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.  SEARCH Response

   Data:       zero or more numbers

      The SEARCH response occurs as a result of a SEARCH or UID SEARCH
      command.  The number(s) refer to those messages that match the
      search criteria.  For SEARCH, these are message sequence numbers;
      for UID SEARCH, these are unique identifiers.  Each number is
      delimited by a space.

   Example:    S: * SEARCH 2 3 6


7.2.5.  FLAGS Response

   Data:       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 may 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)



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7.3.    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 either a message sequence number or a message
   count.

7.3.1.  EXISTS Response

   Data:       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


7.3.2.  RECENT Response

   Data:       none

      The RECENT response reports the number of messages that have
      arrived since the previous time a SELECT command was done on this
      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 RECENT response MUST be recorded by the
      client.

   Example:    S: * 5 RECENT


7.3.3.  EXPUNGE Response

   Data:       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).




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      As a result of the immediate decrement rule, message sequence
      numbers that appear in a set of successive EXPUNGE responses
      depend upon whether the messages are removed starting from lower
      numbers to higher numbers, or from higher numbers to lower
      numbers.  For example, if the last 5 messages in a 9-message
      mailbox are expunged; a "lower to higher" server will send five
      untagged EXPUNGE responses for message sequence number 5, whereas
      a "higher to lower server" will send successive untagged EXPUNGE
      responses for message sequence numbers 9, 8, 7, 6, and 5.

      An EXPUNGE response MUST NOT be sent when no command is in
      progress; nor while responding to a FETCH, STORE, or SEARCH
      command.  This rule is necessary to prevent a loss of
      synchronization of message sequence numbers between client and
      server.

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

   Example:    S: * 44 EXPUNGE


7.3.4.  FETCH Response

   Data:       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]  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.

                     8-bit textual data is permitted if a character set
                     identifier is part of the body parameter
                     parenthesized list for this section.

                     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



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                     original binary data, the client must decode the
                     transfer encoded string.

      BODYSTRUCTURE  A parenthesized list that describes the body
                     structure of a message.  This is computed by the
                     server by parsing the [RFC-822] header and body
                     into the component parts, defaulting various fields
                     as necessary.

                     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.).

                     Extension data follows the multipart subtype.
                     Extension data is never returned with the BODY
                     fetch, but may be returned with a BODYSTRUCTURE
                     fetch.  Extension data, if present, must be in the
                     defined order.

                     The extension data of a multipart body part are in
                     the following order:

                     body parameter parenthesized list
                        A parenthesized list of attribute/value pairs
                        [e.g. (foo bar baz rag) where "bar" is the value
                        of "foo" and "rag" is the value of "baz"] as
                        defined in [MIME-1].

                     Any following extension data are not yet defined in
                     this version of the protocol.  Such extension data
                     may 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 type name as defined
                        in [MIME-1].




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                     body subtype
                        A string giving the content subtype name as
                        defined in [MIME-1].

                     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-1].

                     body id
                        A string giving the content id as defined in
                        [MIME-1].

                     body description
                        A string giving the content description as
                        defined in [MIME-1].

                     body encoding
                        A string giving the content transfer encoding as
                        defined in [MIME-1].

                     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
                     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 may 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:




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                     body MD5
                        A string giving the content MD5 value as defined
                        in [MIME-1].

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

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










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      FLAGS          A parenthesized list of flags that are set for this
                     message.  This may include keywords as well as the
                     following system flags:

                     \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).

                     as well as the following special flag, which may be
                     fetched but not stored:

                     \Recent     Message has arrived since the previous
                                 time this mailbox was selected.

      INTERNALDATE   A string containing the date and time of final
                     delivery of the message as defined by [SMTP].

      RFC822         A string expressing the message in [RFC-822]
                     format.  The header portion of the message must be
                     7-bit.  8-bit characters are permitted only in the
                     non-header portion of the message only if there are
                     [MIME-1] data in the message that identify the
                     character set of the message.

      RFC822.HEADER  A string expressing the [RFC-822] format header of
                     the message, including the delimiting blank line
                     between the header and the body.  The entire string
                     must be 7-bit; 8-bit characters are not permitted
                     in headers.  RFC822.HEADER is used to return data
                     for the RFC822.HEADER, RFC822.HEADER.LINES, and
                     RFC822.HEADER.LINES.NOT FETCH data items.  Note
                     that a blank line is always included regardless of
                     header line restrictions.

      RFC822.SIZE    A number expressing the number of octets in the
                     message in [RFC-822] format.






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      RFC822.TEXT    A string expressing the text body of the message,
                     omitting the [RFC-822] header.  8-bit characters
                     are permitted only if there are [MIME-1] data in
                     the message that identify the character set of the
                     message.

      UID            A number expressing the unique identifier of the
                     message.


   Example:    S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)


7.3.5.  Obsolete Responses

   In addition to the responses listed in here, client implementations
   MUST accept and implement the obsolete responses described in
   Appendix B.



7.4.    Server Responses - Command Continuation Request

   The command completion 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"



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8.      Sample IMAP4 session

   The following is a transcript of an IMAP4 session.  A long line in
   this sample is broken for editorial clarity.

   S:   * OK IMAP4 Service Ready
   C:   a001 login mrc secret
   S:   a001 OK LOGIN completed
   C:   a002 select inbox
   S:   * 18 EXISTS
   S:   * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
   S:   * 2 RECENT
   S:   * OK [UNSEEN 17] Message 17 is the first unseen message
   S:   * OK [UIDVALIDITY 3857529045] UIDs valid
   S:   a002 OK [READ-WRITE] SELECT completed
   C:   a003 fetch 12 full
   S:   * 12 FETCH (FLAGS (\Seen) INTERNALDATE "14-Jul-1993 02:44:25 -0700"
         RFC822.SIZE 4282 ENVELOPE ("Wed, 14 Jul 1993 02:23:25 -0700 (PDT)"
         "IMAP4 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 rfc822.header
   S:    * 12 FETCH (RFC822.HEADER {346}
   S:    Date: Wed, 14 Jul 1993 02:23:25 -0700 (PDT)
   S:    From: Terry Gray <gray@cac.washington.edu>
   S:    Subject: IMAP4 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 IMAP4 server terminating connection
   S:    a006 OK LOGOUT completed




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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 a comma.

   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.

   Syntax marked as obsolete may be encountered with implementations
   written for an earlier version of this protocol (e.g. IMAP2).  New
   implementations SHOULD accept obsolete syntax as input, but MUST NOT
   otherwise use such syntax.

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

   addr_adl        ::= nstring

   addr_host       ::= nstring
                       ;; NIL indicates [RFC-822] group syntax

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

   addr_name       ::= nstring

   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





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   atom            ::= 1*ATOM_CHAR

   ATOM_CHAR       ::= <any CHAR except atom_specials>

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

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

   auth_type       ::= atom

   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 1#body_extension]
                       ;; MUST NOT be returned on non-extensible
                       ;; "BODY" fetch

   body_ext_mpart  ::= body_fld_param [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_enc    ::= (<"> ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
                       "QUOTED-PRINTABLE") <">) / string

   body_fld_id     ::= nstring

   body_fld_lines  ::= number




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   body_fld_md5    ::= nstring

   body_fld_octets ::= number

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

   body_fld_subtyp ::= string

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

   body_type_basic ::= (<"> ("APPLICATION" / "AUDIO" / "IMAGE" /
                       "MESSAGE" / "VIDEO") <">) / string) SPACE
                       body_fld_subtyp SPACE body_fields
                       ;; MESSAGE subtype MUST NOT be "RFC822"

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

   body_type_msg   ::= <"> "MESSAGE" <"> SPACE <"> "RFC822" <"> SPACE
                       body_fields SPACE envelope SPACE body SPACE
                       body_fld_lines

   body_type_text  ::= <"> "TEXT" <"> SPACE body_fld_subtyp SPACE
                        body_fields SPACE body_fld_lines

   capability      ::= atom
                       ;; Must begin with "X" or be registered with
                       ;; IANA as standard or standards-track

   capability_data ::= "CAPABILITY" SPACE "IMAP4" [SPACE 1#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 / find / list /
                       lsub / rename / select / 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 / partial / 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, 0x0C>

   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_old)

   date_year       ::= 4digit

   date_year_old   ::= 2digit
                       ;; OBSOLETE, (year - 1900)

   date_time       ::= <"> (date_time_new / date_time_old) <">

   date_time_new   ::= date_day_fixed "-" date_month "-" date_year
                       SPACE time SPACE zone

   date_time_old   ::= date_day_fixed "-" date_month "-" date_year_old
                       SPACE time "-" zone_old
                       ;; OBSOLETE



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   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"

   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       ::= "BODY" / "BODYSTRUCTURE" /
                       "BODY" [".PEEK"] "[" section "]" / "ENVELOPE" /
                       "FLAGS" / "INTERNALDATE" / "UID" /
                       "RFC822" (([".TEXT"] [".PEEK"]) / ".SIZE" /
                       (".HEADER" [".LINES" [".NOT"] SPACE header_list])

   find            ::= "FIND" SPACE ["ALL."] "MAILBOXES" SPACE
                       list_mailbox
                       ;; OBSOLETE




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   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

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

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

   header_line     ::= astring

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

   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; other names may be
                       ;; case-sensitive depending on implementation.

   mailbox_data    ::=  "FLAGS" SPACE flag_list /
                        "LIST" SPACE mailbox_list /
                        "LSUB" SPACE mailbox_list /
                        "MAILBOX" SPACE text /
                        "SEARCH" [SPACE 1#nz_number] /
                        number SPACE "EXISTS" / number SPACE "RECENT"




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

   message_data    ::= nz_number SPACE ("EXPUNGE" /
                       ("FETCH" SPACE msg_fetch) / msg_obsolete)

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

   msg_obsolete    ::= "COPY" / ("STORE" SPACE msg_fetch)
                       ;; OBSOLETE untagged data responses

   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)

   partial         ::= "PARTIAL" SPACE nz_number SPACE
                       ("BODY" [".PEEK"] "[" section "]" /
                       "RFC822" (([".TEXT"] [".PEEK"]) / ".HEADER")
                       SPACE number SPACE number

   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



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   response        ::= *response_data response_done

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

   response_done   ::= response_tagged / response_fatal

   response_fatal  ::= "*" SPACE resp_cond_bye CRLF

   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
                       ;; Server will disconnect condition

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

   resp_text       ::= ["[" resp_text_code "]" SPACE] (text_mime2 / text)

   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]
                       search_criteria
                       ;; Character set must be registered with IANA
                       ;; as a MIME character set

   search_criteria ::= 1#search_key

   search_key      ::= search_new / search_old

   search_new      ::= "DRAFT" /
                       "HEADER" SPACE header_line 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 /
                       "UID" SPACE set / "UNDRAFT" / set /
                       "(" search_criteria ")"
                       ;; New in IMAP4



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   search_old      ::= "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"
                       ;; Defined in [IMAP2]

   section         ::= "0" / nz_number ["." section]

   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>

   store           ::= "STORE" SPACE set SPACE store_att_flags

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

   string          ::= quoted / literal

   subscribe       ::= ("SUBSCRIBE" SPACE mailbox) / subscribe_obs

   subscribe_obs   ::= "SUBSCRIBE" SPACE "MAILBOX" SPACE mailbox
                       ;;OBSOLETE




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

   text            ::= 1*TEXT_CHAR

   text_mime2       ::= "=?" <charset> "?" <encoding> "?"
                        <encoded-text> "?="
                        ;; Syntax defined in [MIME-2]

   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) / unsubscribe_obs

   unsubscribe_obs ::= "UNSUBSCRIBE" SPACE "MAILBOX" SPACE mailbox
                       ;;OBSOLETE

   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".















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   zone_old        ::= "UT" / "GMT" / "Z" /                ;; +0000
                       "AST" / "EDT" /                     ;; -0400
                       "EST" / "CDT" /                     ;; -0500
                       "CST" / "MDT" /                     ;; -0600
                       "MST" / "PDT" /                     ;; -0700
                       "PST" / "YDT" /                     ;; -0800
                       "YST" / "HDT" /                     ;; -0900
                       "HST" / "BDT" /                     ;; -1000
                       "BST" /                             ;; -1100
                       "A" / "B" / "C" / "D" / "E" / "F" / ;; +1 to +6
                       "G" / "H" / "I" / "K" / "L" / "M" / ;; +7 to +12
                       "N" / "O" / "P" / "Q" / "R" / "S" / ;; -1 to -6
                       "T" / "U" / "V" / "W" / "X" / "Y"   ;; -7 to -12
                       ;; OBSOLETE





































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10.     Author's Note

   This document is a revision or rewrite of earlier documents, and
   supercedes the protocol specification in those documents: IMAP4
   Internet drafts, the IMAP2bis Internet drafts, unpublished
   IMAP2bis.TXT document, RFC 1176, and RFC 1064.


11.     Security Considerations

   IMAP4 protocol transactions, including electronic mail data, are sent
   in the clear over the network unless the optional 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.

   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, JE-30
   University of Washington
   Seattle, WA  98195

   Phone: (206) 543-5762

   EMail: MRC@CAC.Washington.EDU













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RFC 1730                         IMAP4                     December 1994


Appendices

A.      Obsolete Commands

   The following commands are OBSOLETE.  It is NOT required to support
   any of these commands in new server implementations.  These commands
   are documented here for the benefit of implementors who may wish to
   support them for compatibility with old client implementations.

   The section headings of these commands are intended to correspond
   with where they would be located in the main document if they were
   not obsoleted.


A.6.3.OBS.1.    FIND ALL.MAILBOXES Command

   Arguments:  mailbox name with possible wildcards

   Data:       untagged responses: MAILBOX

   Result:     OK - find completed
               NO - find failure: can't list that name
               BAD - command unknown or arguments invalid

      The FIND ALL.MAILBOXES command returns a subset of names from the
      complete set of all names available to the user.  It returns zero
      or more untagged MAILBOX replies.  The mailbox argument to FIND
      ALL.MAILBOXES is similar to that for LIST with an empty reference,
      except that the characters "%" and "?" match a single character.

   Example:    C: A002 FIND ALL.MAILBOXES *
               S: * MAILBOX blurdybloop
               S: * MAILBOX INBOX
               S: A002 OK FIND ALL.MAILBOXES completed


A.6.3.OBS.2.    FIND MAILBOXES Command

   Arguments:  mailbox name with possible wildcards

   Data:       untagged responses: MAILBOX

   Result:     OK - find completed
               NO - find failure: can't list that name
               BAD - command unknown or arguments invalid

      The FIND MAILBOXES command returns a subset of names from the set
      of names that the user has declared as being "active" or



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      "subscribed".  It returns zero or more untagged MAILBOX replies.
      The mailbox argument to FIND MAILBOXES is similar to that for LSUB
      with an empty reference, except that the characters "%" and "?"
      match a single character.

   Example:    C: A002 FIND MAILBOXES *
               S: * MAILBOX blurdybloop
               S: * MAILBOX INBOX
               S: A002 OK FIND MAILBOXES completed


A.6.3.OBS.3.    SUBSCRIBE MAILBOX Command

   Arguments:  mailbox name

   Data:       no specific data for this command

   Result:     OK - subscribe completed
               NO - subscribe failure: can't subscribe to that name
               BAD - command unknown or arguments invalid

      The SUBSCRIBE MAILBOX command is identical in effect to the
      SUBSCRIBE command.  A server which implements this command must be
      able to distinguish between a SUBSCRIBE MAILBOX command and a
      SUBSCRIBE command with a mailbox name argument of "MAILBOX".

   Example:    C: A002 SUBSCRIBE MAILBOX #news.comp.mail.mime
               S: A002 OK SUBSCRIBE MAILBOX to #news.comp.mail.mime
               completed
               C: A003 SUBSCRIBE MAILBOX
               S: A003 OK SUBSCRIBE to MAILBOX completed


A.6.3.OBS.4.    UNSUBSCRIBE MAILBOX Command

   Arguments:  mailbox name

   Data:       no specific data for this command

   Result:     OK - unsubscribe completed
               NO - unsubscribe failure: can't unsubscribe that name
               BAD - command unknown or arguments invalid

      The UNSUBSCRIBE MAILBOX command is identical in effect to the
      UNSUBSCRIBE command.  A server which implements this command must
      be able to distinguish between a UNSUBSCRIBE MAILBOX command and
      an UNSUBSCRIBE command with a mailbox name argument of "MAILBOX".




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   Example:    C: A002 UNSUBSCRIBE MAILBOX #news.comp.mail.mime
               S: A002 OK UNSUBSCRIBE MAILBOX from #news.comp.mail.mime
               completed
               C: A003 UNSUBSCRIBE MAILBOX
               S: A003 OK UNSUBSCRIBE from MAILBOX completed














































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B.      Obsolete Responses

   The following responses are OBSOLETE.  Except as noted below, these
   responses MUST NOT be transmitted by new server implementations.

   The section headings of these responses are intended to correspond
   with where they would be located in the main document if they were
   not obsoleted.


B.7.2.OBS.1.    MAILBOX Response

   Data:       name

      The MAILBOX response MUST NOT be transmitted by server
      implementations except in response to the obsolete FIND MAILBOXES
      and FIND ALL.MAILBOXES commands.  Client implementations that do
      not use these commands MAY ignore this response.  It is documented
      here for the benefit of implementors who may wish to support it
      for compatibility with old client implementations.

      This response occurs as a result of the FIND MAILBOXES and FIND
      ALL.MAILBOXES commands.  It returns a single name that matches the
      FIND specification.  There are no attributes or hierarchy
      delimiter.

   Example:    S: * MAILBOX blurdybloop


B.7.3.OBS.1.    COPY Response

   Data:       none

      The COPY response MUST NOT be transmitted by new server
      implementations.  Client implementations MUST ignore the COPY
      response.  It is documented here for the benefit of client
      implementors who may encounter this response from old server
      implementations.

      In some experimental versions of this protocol, this response was
      returned in response to a COPY command to indicate on a
      per-message basis that the message was copied successfully.

   Example:    S: * 44 COPY







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B.7.3.OBS.2.    STORE Response

   Data:       message data

      The STORE response MUST NOT be transmitted by new server
      implementations.  Client implementations MUST treat the STORE
      response as equivalent to the FETCH response.  It is documented
      here for the benefit of client implementors who may encounter this
      response from old server implementations.

      In some experimental versions of this protocol, this response was
      returned instead of FETCH in response to a STORE command to report
      the new value of the flags.

   Example:    S: * 69 STORE (FLAGS (\Deleted))




































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C.      References


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

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

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

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

   [IMAP-NAMING] Crispin, M. "Mailbox Naming Convention in IMAP4", Work
   in Progress.

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

   [IMSP] Myers, J. "IMSP -- Internet Message Support Protocol", Work in
   Progress.

   [MIME-1] Borenstein, N., and Freed, N., "MIME (Multipurpose Internet
   Mail Extensions) Part One: Mechanisms for Specifying and Describing
   the Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft,
   September 1993.

   [MIME-2] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
   Part Two: Message Header Extensions for Non-ASCII Text", RFC 1522,
   University of Tennessee, September 1993.

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

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













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E.      IMAP4 Keyword Index


       +FLAGS <flag list> (store command data item) ...............   34
       +FLAGS.SILENT <flag list> (store command data item) ........   34
       -FLAGS <flag list> (store command data item) ...............   34
       -FLAGS.SILENT <flag list> (store command data item) ........   34
       ALERT (response code) ......................................   39
       ALL (fetch item) ...........................................   29
       ALL (search key) ...........................................   27
       ANSWERED (search key) ......................................   27
       APPEND (command) ...........................................   22
       AUTHENTICATE (command) .....................................   12
       BAD (response) .............................................   41
       BCC <string> (search key) ..................................   27
       BEFORE <date> (search key) .................................   27
       BODY (fetch item) ..........................................   29
       BODY (fetch result) ........................................   46
       BODY <string> (search key) .................................   27
       BODY.PEEK[<section>] (fetch item) ..........................   30
       BODYSTRUCTURE (fetch item) .................................   31
       BODYSTRUCTURE (fetch result) ...............................   47
       BODY[<section>] (fetch item) ...............................   29
       BODY[section] (fetch result) ...............................   46
       BYE (response) .............................................   41
       CAPABILITY (command) .......................................   10
       CAPABILITY (response) ......................................   42
       CC <string> (search key) ...................................   27
       CHECK (command) ............................................   23
       CLOSE (command) ............................................   24
       COPY (command) .............................................   34
       COPY (response) ............................................   68
       CREATE (command) ...........................................   17
       DELETE (command) ...........................................   18
       DELETED (search key) .......................................   27
       DRAFT (search key) .........................................   27
       ENVELOPE (fetch item) ......................................   31
       ENVELOPE (fetch result) ....................................   49
       EXAMINE (command) ..........................................   16
       EXISTS (response) ..........................................   45
       EXPUNGE (command) ..........................................   25
       EXPUNGE (response) .........................................   45
       FAST (fetch item) ..........................................   31
       FETCH (command) ............................................   29
       FETCH (response) ...........................................   46
       FIND ALL.MAILBOXES (command) ...............................   65
       FIND MAILBOXES (command) ...................................   65
       FLAGGED (search key) .......................................   27
       FLAGS (fetch item) .........................................   31



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       FLAGS (fetch result) .......................................   50
       FLAGS (response) ...........................................   44
       FLAGS <flag list> (store command data item) ................   34
       FLAGS.SILENT <flag list> (store command data item) .........   34
       FROM <string> (search key) .................................   27
       FULL (fetch item) ..........................................   31
       HEADER <field-name> <string> (search key) ..................   27
       INTERNALDATE (fetch item) ..................................   31
       INTERNALDATE (fetch result) ................................   50
       KEYWORD <flag> (search key) ................................   27
       LARGER <n> (search key) ....................................   27
       LIST (command) .............................................   20
       LIST (response) ............................................   43
       LOGIN (command) ............................................   14
       LOGOUT (command) ...........................................   11
       LSUB (command) .............................................   22
       LSUB (response) ............................................   44
       MAILBOX (response) .........................................   68
       NEW (search key) ...........................................   27
       NO (response) ..............................................   40
       NOOP (command) .............................................   11
       NOT <search-key> (search key) ..............................   28
       OK (response) ..............................................   40
       OLD (search key) ...........................................   28
       ON <date> (search key) .....................................   28
       OR <search-key1> <search-key2> (search key) ................   28
       PARSE (response code) ......................................   39
       PARTIAL (command) ..........................................   32
       PERMANENTFLAGS (response code) .............................   39
       PREAUTH (response) .........................................   41
       READ-ONLY (response code) ..................................   39
       READ-WRITE (response code) .................................   39
       RECENT (response) ..........................................   45
       RECENT (search key) ........................................   28
       RENAME (command) ...........................................   18
       RFC822 (fetch item) ........................................   31
       RFC822 (fetch result) ......................................   50
       RFC822.HEADER (fetch item) .................................   31
       RFC822.HEADER (fetch result) ...............................   50
       RFC822.HEADER.LINES <header_list> (fetch item) .............   31
       RFC822.HEADER.LINES.NOT <header_list> (fetch item) .........   32
       RFC822.PEEK (fetch item) ...................................   31
       RFC822.SIZE (fetch item) ...................................   32
       RFC822.SIZE (fetch result) .................................   50
       RFC822.TEXT (fetch item) ...................................   32
       RFC822.TEXT (fetch result) .................................   51
       RFC822.TEXT.PEEK (fetch item) ..............................   32
       SEARCH (command) ...........................................   25



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       SEARCH (response) ..........................................   44
       SEEN (search key) ..........................................   28
       SELECT (command) ...........................................   15
       SENTBEFORE <date> (search key) .............................   28
       SENTON <date> (search key) .................................   28
       SENTSINCE <date> (search key) ..............................   28
       SINCE <date> (search key) ..................................   28
       SMALLER <n> (search key) ...................................   28
       STORE (command) ............................................   33
       STORE (response) ...........................................   69
       SUBJECT <string> (search key) ..............................   28
       SUBSCRIBE (command) ........................................   19
       SUBSCRIBE MAILBOX (command) ................................   66
       TEXT <string> (search key) .................................   28
       TO <string> (search key) ...................................   28
       TRYCREATE (response code) ..................................   39
       UID (command) ..............................................   35
       UID (fetch item) ...........................................   32
       UID (fetch result) .........................................   51
       UID <message set> (search key) .............................   28
       UIDVALIDITY (response code) ................................   40
       UNANSWERED (search key) ....................................   29
       UNDELETED (search key) .....................................   29
       UNDRAFT (search key) .......................................   29
       UNFLAGGED (search key) .....................................   29
       UNKEYWORD <flag> (search key) ..............................   29
       UNSEEN (response code) .....................................   40
       UNSEEN (search key) ........................................   29
       UNSUBSCRIBE (command) ......................................   19
       UNSUBSCRIBE MAILBOX (command) ..............................   66
       X<atom> (command) ..........................................   37
       \Answered (system flag) ....................................   50
       \Deleted (system flag) .....................................   50
       \Draft (system flag) .......................................   50
       \Flagged (system flag) .....................................   50
       \Marked (mailbox name attribute) ...........................   43
       \Noinferiors (mailbox name attribute) ......................   43
       \Noselect (mailbox name attribute) .........................   43
       \Recent (system flag) ......................................   50
       \Seen (system flag) ........................................   50
       \Unmarked (mailbox name attribute) .........................   43










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