doc: Add RFC documents

1 files changed, 1683 insertions, 0 deletions

diff --git a/doc/rfc/rfc1176.txt b/doc/rfc/rfc1176.txt
new file mode 100644
index 0000000..1ea72a1
--- /dev/null
+++ b/doc/rfc/rfc1176.txt
@@ -0,0 +1,1683 @@
+
+
+
+
+
+
+Network Working Group                                         M. Crispin
+Request for Comments: 1176                                    Washington
+Obsoletes: RFC 1064                                          August 1990
+
+
+              INTERACTIVE MAIL ACCESS PROTOCOL - VERSION 2
+
+
+Status of this Memo
+
+   This RFC suggests a method for personal computers and workstations to
+   dynamically access mail from a mailbox server ("repository").  It
+   obosoletes RFC 1064.  This RFC specifies an Experimental Protocol for
+   the Internet community.  Discussion and suggestions for improvement
+   are requested.  Please refer to the current edition of the "IAB
+   Official Protocol Standards" for the standardization state and status
+   of this protocol.  Distribution of this memo is unlimited.
+
+Introduction
+
+   The intent of the Interactive Mail Access Protocol, Version 2 (IMAP2)
+   is to allow a workstation, personal computer, or similar small
+   machine to access electronic mail from a mailbox server.  Since the
+   distinction between personal computers and workstations is blurring
+   over time, it is desirable to have a single solution that addresses
+   the need in a general fashion.  IMAP2 is the "glue" of a distributed
+   electronic mail system consisting of a family of client and server
+   implementations on a wide variety of platforms, from small single-
+   tasking personal computing engines to complex multi-user timesharing
+   systems.
+
+   Although different in many ways from the Post Office Protocols (POP2
+   and POP3, hereafter referred to collectively as "POP") described in
+   RFC 937 and RFC 1081, IMAP2 may be thought of as a functional
+   superset of these.  RFC 937 was used as a model for this RFC.  There
+   was a cognizant reason for this; POP deals with a similar problem,
+   albeit with a less comprehensive solution, and it was desirable to
+   offer a basis for comparison.
+
+   Like POP, IMAP2 specifies a means of accessing stored mail and not of
+   posting mail; this function is handled by a mail transfer protocol
+   such as SMTP (RFC 821).
+
+   This protocol assumes a reliable data stream such as provided by TCP
+   or any similar protocol.  When TCP is used, the IMAP2 server listens
+   on port 143.
+
+
+
+
+
+Crispin                                                         [Page 1]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+System Model and Philosophy
+
+   Electronic mail is a primary means of communication for the widely
+   spread Internet community.  The advent of distributed personal
+   computers and workstations has forced a significant rethinking of the
+   mechanisms employed to manage electronic mail.  With mainframes, each
+   user tends to receive and process mail at the computer he uses most
+   of the time, his "primary host".  The first inclination of many users
+   when an independent workstation is placed in front of them is to
+   begin receiving mail at the workstation, and many vendors have
+   implemented facilities to do this.  However, this approach has
+   several disadvantages:
+
+      (1) Personal computers and many workstations have a software
+      design that gives full control of all aspects of the system to the
+      user at the console.  As a result, background tasks such as
+      receiving mail may not run for long periods of time; either
+      because the user is asking to use all the machine's resources, or
+      because the user has (perhaps accidentally) manipulated the
+      environment in such a way that it prevents mail reception.  In
+      many personal computers, the operating system is single-tasking
+      and this is the only mode of operation.  Any of these conditions
+      could lead to repeated failed delivery attempts by outside agents.
+
+      (2) The hardware failure of a single machine can keep its user
+      "off the air" for a considerable time, since repair of individual
+      units may be delayed.  Given the growing number of personal
+      computers and workstations spread throughout office environments,
+      quick repair of such systems is not assured.  On the other hand, a
+      central mainframe is generally repaired soon after failure.
+
+      (3) Personal computers and workstations are often not backed up
+      with as much diligence as a central mainframe, if at all.
+
+      (4) It is more difficult to keep track of mailing addresses when
+      each person is associated with a distinct machine.  Consider the
+      difficulty in keeping track of many postal addresses or phone
+      numbers, particularly if there was no single address or phone
+      number for an organization through which you could reach any
+      person in that organization.  Traditionally, electronic mail on
+      the ARPANET involved remembering a name and one of several "hosts"
+      (machines) whose name reflected the organization in which the
+      individual worked.  This was suitable at a time when most
+      organizations had only one central host.  It is less satisfactory
+      today unless the concept of a host is changed to refer to an
+      organizational entity and not a particular machine.
+
+      (5) It is difficult to keep a multitude of heterogeneous machines
+
+
+
+Crispin                                                         [Page 2]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      working properly with complex mailing protocols, making it
+      difficult to move forward as progress is made in electronic
+      communication and as new standards emerge.  Each system has to
+      worry about receiving incoming mail, routing and delivering
+      outgoing mail, formatting, storing, and providing for the
+      stability of mailboxes over a variety of possible filing and
+      mailing protocols.
+
+   Consequently, while a personal computer or workstation may be viewed
+   as an Internet host in the sense that it implements TCP/IP, it should
+   not be viewed as the entity that contains the user's mailbox.
+   Instead, a mail server machine ("server", sometimes called a
+   "repository") should hold the mailbox, and the personal computer or
+   workstation (hereafter referred to as a "client") should access the
+   mailbox via mail transactions.
+
+   Because the mail server machine is isolated from direct user
+   manipulation, it should achieve high software reliability easily,
+   and, as a shared resource, it should also achieve high hardware
+   reliability, perhaps through redundancy.  The mail server may be
+   accessed from arbitrary locations, allowing users to read mail across
+   campus, town, or country using commonly available clients.
+   Furthermore, the same user may access his mailbox from different
+   clients at different times, and multiple users may access the same
+   mailbox simultaneously.
+
+   The mail server acts an an interface among users, data storage, and
+   other mailers.  A mail access protocol retrieves messages, accesss
+   and changes properties of messages, and otherwise manages mailboxes.
+   This differs from some approaches (e.g., Unix mail via NFS) in that
+   the mail access protocol is used for all message manipulations,
+   isolating the user and the client from all knowledge of how the data
+   storage is used.  This means that the mail server can use the data
+   storage in whatever way is most efficient to organize the mail in
+   that particular environment, without having to worry about storage
+   representation compatibility across different machines.
+
+   A mail access protocol further differs in that it transmits
+   information only on demand.  A well-designed mail access protocol
+   requires considerably less network traffic than Unix mail via NFS,
+   particularly when the mail file is large.  The result is that a mail
+   access protocol can scale well to situations of large mailboxes or
+   networks with high latency or low speed.
+
+   In defining a mail access protocol, it is important to keep in mind
+   that the client and server form a macrosystem, in which it should be
+   possible to exploit the strong points of both while compensating for
+   each other's weaknesses.  Furthermore, it is desirable to allow for a
+
+
+
+Crispin                                                         [Page 3]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   growth path beyond the hoary text-only RFC 822 protocol, specifically
+   in the area of attachments and multi-media mail, to ease the eventual
+   transition to ISO solutions.
+
+   Unlike POP, IMAP2 has extensive features for remote searching and
+   parsing of messages on the server.  A free text search (optionally
+   with other searching) can be made in the entire mailbox by the server
+   and the results made available to the client without the client
+   having to transfer the entire mailbox and searching itself.  Since
+   remote parsing of a message into a structured (and standard format)
+   "envelope" is available, a client can display envelope information
+   and implement commands such as REPLY without having any understanding
+   of how to parse RFC 822, etc. headers.  The effect of this is
+   twofold: it further improves the ability to scale well in instances
+   where network traffic must be reduced, and it reduces the complexity
+   of the client program.
+
+   Additionally, IMAP2 offers several facilities for managing individual
+   message state and the mailbox as a whole beyond the simple "delete
+   message" functionality of POP.  Another benefit of IMAP2 is the use
+   of tagged responses to reduce the possibility of synchronization
+   errors and the concept of state on the client (a "local cache") that
+   the server may update without explicit request by the client.  These
+   concepts and how they are used are explained under "Implementation
+   Discussion" below.
+
+   In spite of this functional richness, IMAP2 is a small protocol.
+   Although servers should implement the full set of IMAP2 functions, a
+   simple client can be written that uses IMAP2 in much the way as a POP
+   client.
+
+   A related protocol to POP and IMAP2 is the DMSP protocol of PCMAIL
+   (RFC 1056).  IMAP2 differs from DMSP more fundamentally, reflecting a
+   differing architecture from PCMAIL.  PCMAIL is either an online
+   ("interactive mode"), or offline ("batch mode") system with long-term
+   shared state.  Some POP based systems are also offline; in such
+   systems, since there is no long-term shared state POP is little more
+   than a download mechanism of the "mail file" to the client.  IMAP2-
+   based software is primarily an online system in which real-time and
+   simultaneous mail access were considered important.
+
+   In PCMAIL, there is a long-term client/server relationship in which
+   some mailbox state is preserved on the client.  There is a
+   registration of clients used by a particular user, and the client
+   keeps a set of "descriptors" for each message that summarize the
+   message.  The server and client synchronize their states when the
+   DMSP connection starts up, and, if a client has not accessed the
+   server for a while, the client does a complete reset (reload) of its
+
+
+
+Crispin                                                         [Page 4]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   state from the server.
+
+   In IMAP2-based software, the client/server relationship lasts only
+   for the duration of the TCP connection.  All mailbox state is
+   maintained on the server.  There is no registration of clients.  The
+   function of a descriptor is handled by a structured representation of
+   the message "envelope" as noted above.  There is no client/server
+   synchronization since the client does not remember state between
+   IMAP2 connections.  This is not a problem since in general the client
+   never needs the entire state of the mailbox in a single session,
+   therefore there isn't much overhead in fetching the state information
+   that is needed as it is needed.
+
+   There are also some functional differences between IMAP2 and DMSP.
+   DMSP has functions for sending messages, printing messages, listing
+   mailboxes, and changing passwords; these are done outside IMAP2.
+   DMSP has 16 binary flags of which 8 are defined by the system.  IMAP2
+   has flag names; there are currently 5 defined system flag names and a
+   facility for some number (30 in the current implementations) of user
+   flag names.  IMAP2 has a sophisticated message search facility in the
+   server to identify interesting messages based on dates, addresses,
+   flag status, or textual contents without compelling the client to
+   fetch this data for every message.
+
+   It was felt that maintaining state on the client is advantageous only
+   in those cases where the client is only used by a single user, or if
+   there is some means on the client to restrict access to another
+   user's data.  It can be a serious disadvantage in an environment in
+   which multiple users routinely use the same client, the same user
+   routinely uses different clients, and where there are no access
+   restrictions on the client.  It was also observed that most user mail
+   access is to a small set of "interesting" messages, which were either
+   new mail or mail based on some user-selected criteria.  Consequently,
+   IMAP2 was designed to easily identify those "interesting" messages so
+   that the client could fetch the state of those messages and not those
+   that were not "interesting".
+
+The Protocol
+
+   The IMAP2 protocol consists of a sequence of client commands and
+   server responses, with server data interspersed between the
+   responses.  Unlike most Internet protocols, commands and responses
+   are tagged.  That is, a command begins with a unique identifier
+   (typically a short alphanumeric sequence such as a Lisp "gensym"
+   function would generate e.g., A0001, A0002, etc.), called a tag.  The
+   response to this command is given the same tag from the server.
+   Additionally, the server may send an arbitrary amount of "unsolicited
+   data", which is identified by the special reserved tag of "*".  There
+
+
+
+Crispin                                                         [Page 5]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   is another special reserved tag, "+", discussed below.
+
+   The server must be listening for a connection.  When a connection is
+   opened the server sends an unsolicited OK response as a greeting
+   message and then waits for commands.
+
+   The client opens a connection and waits for the greeting.  The client
+   must not send any commands until it has received the greeting from
+   the server.
+
+   Once the greeting has been received, the client may begin sending
+   commands and is not under any obligation to wait for a server
+   response to this command before sending another command, within the
+   constraints of TCP flow control.  When commands are received the
+   server acts on them and responds with command responses, often
+   interspersed with data.  The effect of a command can not be
+   considered complete until a command response with a tag matching the
+   command is received from the server.
+
+   Although all known IMAP2 servers at the time of this writing process
+   commands to completion before processing the next command, it is not
+   required that a server do so.  However, many commands can affect the
+   results of other commands, creating processing-order dependencies
+   (or, for SEARCH and FIND, ambiguities about which data is associated
+   with which command).  All implementations that operate in a non-
+   lockstep fashion must recognize such dependencies and defer or
+   synchronize execution as necessary.  In general, such multi-
+   processing is limited to consecutive FETCH commands.
+
+   Generally, the first command from the client is a LOGIN command with
+   user name and password arguments to establish identity and access
+   authorization, unless this has already been accomplished through
+   other means, e.g. Kerberos.  Until identity and access authorization
+   have been established, no operations other than LOGIN or LOGOUT are
+   permitted.
+
+   Once identity and authorization have been established, the client
+   must send a SELECT command to access the desired mailbox; no mailbox
+   is selected by default.  SELECT's argument is implementation-
+   dependent; however the word "INBOX" must be implemented to mean the
+   primary or default mailbox for this user, independent of any other
+   server semantics.  On a successful SELECT, the server will send a
+   list of valid flags, number of messages, and number of messages
+   arrived since last access for this mailbox as unsolicited data,
+   followed by an OK response.  The client may terminate access to this
+   mailbox and access a different one with another SELECT command.
+
+   The client reads mailbox information with FETCH commands.  The actual
+
+
+
+Crispin                                                         [Page 6]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   data is transmitted via the unsolicited data mechanism (that is,
+   FETCH should be viewed as instructing the server to include the
+   desired data along with any other data it wishes to transmit to the
+   client).  There are three major categories of data that may be
+   fetched.
+
+   The first category is data that is associated with a message as an
+   entity in the mailbox.  There are now three such items of data: the
+   "internal date", the "RFC 822 size", and the "flags".  The internal
+   date is the date and time that the message was placed in the mailbox.
+   The RFC 822 size is subject to deletion in the future; it is the size
+   in bytes of the message, expressed as an RFC 822 text string.
+   Current clients only use it as part of a status display line.  The
+   flags are a list of status flags associated with the message (see
+   below).  All the first category data can be fetched by using the
+   macro-fetch word "FAST"; that is, "FAST" expands to "(FLAGS
+   INTERNALDATE RFC822.SIZE)".
+
+   The second category is that data that describes the composition and
+   delivery information of a message; that is, information such as the
+   message sender, recipient lists, message-ID, subject, etc.  This is
+   the information that is stored in the message header in RFC 822
+   format message and is traditionally called the "envelope".  [Note:
+   this should not be confused with the SMTP (RFC 821) envelope, which
+   is strictly limited to delivery information.]  IMAP2 defines a
+   structured and unambiguous representation for the envelope that is
+   particularly suited for Lisp-based parsers.  A client can use the
+   envelope for operations such as replying and not worry about RFC 822
+   at all.  Envelopes are discussed in more detail below.  The first two
+   categories of data can be fetched together by using the macro-fetch
+   word "ALL"; that is, "ALL" expands to "(FLAGS INTERNALDATE
+   RFC822.SIZE ENVELOPE)".
+
+   The third category is that data that is intended for direct human
+   viewing.  The present RFC 822 based IMAP2 defines three such items:
+   RFC822.HEADER, RFC822.TEXT, and RFC822 (the latter being the two
+   former appended together in a single text string).  RFC822.HEADER is
+   the "raw", unprocessed RFC 822 format header of the message.
+   Fetching "RFC822" is equivalent to fetching the RFC 822
+   representation of the message as stored on the mailbox without any
+   filtering or processing.
+
+   An intelligent client will "FETCH ALL" for some (or all) of the
+   messages in the mailbox for use as a presentation menu, and when the
+   user wishes to read a particular message will "FETCH RFC822.TEXT" to
+   get the message body.  A more primitive client could, of course,
+   simply "FETCH RFC822" a`la POP-type functionality.
+
+
+
+
+Crispin                                                         [Page 7]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   The client can alter certain data (currently only the flags) by a
+   STORE command.  As an example, a message is deleted from a mailbox by
+   a STORE command that includes the \DELETED flag as a flag being set.
+
+   Other client operations include copying a message to another mailbox
+   (COPY command), permanently removing deleted messages (EXPUNGE
+   command), checking for new messages (CHECK command), and searching
+   for messages that match certain criteria (SEARCH command).
+
+   The client terminates the session with the LOGOUT command.  The
+   server returns a "BYE" followed by an "OK".
+
+   A Typical Scenario
+
+           Client                          Server
+           ------                          ------
+                                       {Wait for Connection}
+       {Open Connection}        -->
+                                   <-- * OK IMAP2 Server Ready
+                                       {Wait for command}
+       A001 LOGIN Fred Secret   -->
+                                   <-- A001 OK User Fred logged in
+                                       {Wait for command}
+       A002 SELECT INBOX        -->
+                                   <-- * FLAGS (Meeting Notice \Answered
+                                                \Flagged \Deleted \Seen)
+                                   <-- * 19 EXISTS
+                                   <-- * 2 RECENT
+                                   <-- A0002 OK Select complete
+                                       {Wait for command}
+       A003 FETCH 1:19 ALL      -->
+                                   <-- * 1 Fetch (......)
+                                           ...
+                                   <-- * 18 Fetch (......)
+                                   <-- * 19 Fetch (......)
+                                   <-- A003 OK Fetch complete
+                                       {Wait for command}
+       A004 FETCH 8 RFC822.TEXT -->
+                                   <-- * 8 Fetch (RFC822.TEXT {893}
+                                           ...893 characters of text...
+                                   <-- )
+                                   <-- A004 OK Fetch complete
+                                       {Wait for command}
+
+
+
+
+
+
+
+
+Crispin                                                         [Page 8]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+       A005 STORE 8 +Flags \Deleted -->
+                                   <-- * 8 Store (Flags (\Deleted
+                                                  \Seen))
+                                   <-- A005 OK Store complete
+                                       {Wait for command}
+       A006 EXPUNGE             -->
+                                   <-- * 19 EXISTS
+                                   <-- * 8 EXPUNGE
+                                   <-- * 18 EXISTS
+                                   <-- A006 Expunge complete
+                                       {Wait for command}
+       A007 LOGOUT              -->
+                                   <-- * BYE IMAP2 server quitting
+                                   <-- A007 OK Logout complete
+       {Close Connection}       --><-- {Close connection}
+                                       {Go back to start}
+Conventions
+
+   The following terms are used in a meta-sense in the syntax
+   specification below:
+
+      An ASCII-STRING is a sequence of arbitrary ASCII characters.
+
+      An ATOM is a sequence of ASCII characters delimited by SP or CRLF.
+
+      A CHARACTER is any ASCII character except """", "{", CR, LF, "%",
+      or "\".
+
+      A CRLF is an ASCII carriage-return character followed immediately
+      by an ASCII linefeed character.
+
+      A NUMBER is a sequence of the ASCII characters that represent
+      decimal numerals ("0" through "9"), delimited by SP, CRLF, ",", or
+      ":".
+
+      A SP is the ASCII space character.
+
+      A TEXT_LINE is a human-readable sequence of ASCII characters up to
+      but not including a terminating CRLF.
+
+   A common field in the IMAP2 protocol is a STRING, which may be an
+   ATOM, QUOTED-STRING (a sequence of CHARACTERs inside double-quotes),
+   or a LITERAL.  A literal consists of an open brace ("{"), a number, a
+   close brace ("}"), a CRLF, and then an ASCII-STRING of n characters,
+   where n is the value of the number inside the brace.  In general, a
+   string should be represented as an ATOM or QUOTED-STRING if at all
+   possible.  The semantics for QUOTED-STRING or LITERAL are checked
+   before those for ATOM; therefore an ATOM used in a STRING may only
+
+
+
+Crispin                                                         [Page 9]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   contain CHARACTERs.  Literals are most often sent from the server to
+   the client; in the rare case of a client to server literal there is a
+   special consideration (see the "+ text" response below).
+
+   Another important field is the SEQUENCE, which identifies a set of
+   messages by consecutive numbers from 1 to n where n is the number of
+   messages in the mailbox.  A sequence may consist of a single number,
+   a pair of numbers delimited by colon (equivalent to all numbers
+   between those two numbers), or a list of single numbers or number
+   pairs.  For example, the sequence 2,4:7,9,12:15 is equivalent to
+   2,4,5,6,7,9,12,13,14,15 and identifies all those messages.
+
+Definitions of Commands and Responses
+
+     Summary of Commands and Responses
+
+       Commands                            ||      Responses
+       --------                            ||      -------
+       tag NOOP                            ||      tag OK text
+       tag LOGIN user password             ||      tag NO text
+       tag LOGOUT                          ||      tag BAD text
+       tag SELECT mailbox                  ||      * number message_data
+       tag BBOARD bulletin_board           ||      * FLAGS flag_list
+       tag FIND MAILBOXES pattern          ||      * SEARCH sequence
+       tag FIND BBOARDS pattern            ||      * BBOARD string
+       tag CHECK                           ||      * MAILBOX string
+       tag EXPUNGE                         ||      * BYE text
+       tag COPY sequence mailbox           ||      * OK text
+       tag FETCH sequence data             ||      * NO text
+       tag STORE sequence data value       ||      * BAD text
+       tag SEARCH search_program           ||      + text
+
+Commands
+
+   tag NOOP
+
+      The NOOP command returns an OK to the client.  By itself, it does
+      nothing, but certain things may happen as side effects.  For
+      example, server implementations that implicitly check the mailbox
+      for new mail may do so as a result of this command.  The primary
+      use of this command is to for the client to see if the server is
+      still alive (and notify the server that the client is still alive,
+      for those servers that have inactivity autologout timers).
+
+   tag LOGIN user password
+
+      The LOGIN command identifies the user to the server and carries
+      the password authenticating this user.  This information is used
+
+
+
+Crispin                                                        [Page 10]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      by the server to control access to the mailboxes.
+
+      EXAMPLE:  A001 LOGIN SMITH SESAME
+      logs in as user SMITH with password SESAME.
+
+   tag LOGOUT
+
+      The LOGOUT command informs the server that the client is done with
+      the session.  The server should send an unsolicited BYE response
+      before the (tagged) OK response, and then close the network
+      connection.
+
+   tag SELECT mailbox
+
+      The SELECT command selects a particular mailbox.  The server must
+      check that the user is permitted read access to this mailbox.
+      Before returning an OK to the client, the server must send the
+      following unsolicited data to the client:
+         FLAGS        mailbox's defined flags
+         <n> EXISTS   the number of messages in the mailbox
+         <n> RECENT   the number of new messages in the mailbox
+      in order to define the initial state of the mailbox at the client.
+
+      Multiple SELECT commands are permitted in a session, in which case
+      the previous mailbox is automatically deselected when a new SELECT
+      is made.
+
+      The default mailbox for the SELECT command is INBOX, which is a
+      special name reserved to mean "the primary mailbox for this user
+      on this server".  The format of other mailbox names is operating
+      system dependent (as of this writing, it reflects the filename
+      path of the mailbox file on the current servers).
+
+      It is customary, although not required, for the text of an OK
+      response to the SELECT command to begin with either "[READ-ONLY]"
+      or "[READ-WRITE]" to show the mailbox's access status.
+
+      EXAMPLE: A002 SELECT INBOX
+      selects the default mailbox.
+
+   tag BBOARD bulletin_board
+
+      The BBOARD command is equivalent to SELECT, and returns the same
+      output.  However, it differs from SELECT in that its argument is a
+      shared mailbox (bulletin board) name instead of an ordinary
+      mailbox.  The format of a bulletin name is implementation
+      specific, although it is strongly encouraged to use something that
+      resembles a name in a generic sense and not a file or mailbox name
+
+
+
+Crispin                                                        [Page 11]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      on the particular system.  There is no requirement that a bulletin
+      board name be a mailbox name or a file name (in particular, Unix
+      netnews has a completely different namespace from mailbox or file
+      names).
+
+      Support for BBOARD is optional.
+
+   tag FIND MAILBOXES pattern
+
+      The FIND MAILBOXES command accepts as an argument a pattern
+      (including wildcards) that specifies some set of mailbox names
+      that are usable by the SELECT command.  The format of mailboxes is
+      implementation dependent.  The special mailbox name INBOX is not
+      included in the output.
+
+      Two wildcard characters are defined; "*" specifies any number
+      (including zero) characters may match at this position and "%"
+      specifies a single character may match at this position.  For
+      example, FOO*BAR will match FOOBAR, FOOD.ON.THE.BAR and FOO.BAR,
+      whereas FOO%BAR will match only FOO.BAR.  "*" will match all
+      mailboxes.
+
+      The FIND MAILBOXES command will return some set of unsolicited
+      MAILBOX replies that have as their value a single mailbox name.
+
+      EXAMPLE:  A002 FIND MAILBOXES *
+                * MAILBOX FOOBAR
+                * MAILBOX GENERAL
+                A002 FIND completed
+
+      Although the use of explicit file or path names for mailboxes is
+      discouraged by this standard, it may be unavoidable.  It is
+      important that the value returned in the MAILBOX unsolicited reply
+      be usable in the SELECT command without remembering any path
+      specification that may have been used in the FIND MAILBOXES
+      pattern.
+
+      Support for FIND MAILBOXES is optional.  If a client's attempt
+      returns BAD as a response then the client can make no assumptions
+      about what mailboxes exist on the server other than INBOX.
+
+   tag FIND BBOARDS pattern
+
+      The FIND BBOARDS command accepts as an argument a pattern that
+      specifies some set of bulletin board names that are usable by the
+      BBOARD command.  Wildcards are permitted as in FIND MAILBOXES.
+
+      The FIND BBOARDS command will return some set of unsolicited
+
+
+
+Crispin                                                        [Page 12]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      BBOARD replies that have as their value a single bulletin board
+      name.
+
+      EXAMPLE:  A002 FIND BBOARDS *
+                * BBOARD FOOBAR
+                * BBOARD GENERAL
+                A002 FIND completed
+
+      Support for FIND BBOARDS is optional.  If a client's attempt
+      returns BAD as a response then the client can make no assumptions
+      about what bulletin boards exist on the server, or that they exist
+      at all.
+
+   tag CHECK
+
+      The CHECK command forces a check for new messages and a rescan of
+      the mailbox for internal change for those implementations that
+      allow multiple simultaneous read/write access to the same mailbox.
+      It is recommend that periodic implicit checks for new mail be done
+      by servers as well.  The server should send unsolicited EXISTS and
+      RECENT responses with the current status before returning an OK to
+      the client.
+
+   tag EXPUNGE
+
+      The EXPUNGE command permanently removes all messages with the
+      \DELETED flag set in its flags from the mailbox.  Before returning
+      an OK to the client, for each message that is removed, an
+      unsolicited EXPUNGE response is sent.  The message number for each
+      successive message in the mailbox is immediately decremented by 1;
+      this means that if the last 5 messages in a 9-message mail file
+      are expunged you will receive 5 unsolicited EXPUNGE responses for
+      message 5.  To ensure mailbox integrity and server/client
+      synchronization, it is recommended that the server do an implicit
+      check before commencing the expunge and again when the expunge is
+      completed.  Furthermore, if the server allows multiple
+      simultaneous access to the same mail file the server must lock the
+      mail file for exclusive access while an expunge is taking place.
+
+      EXPUNGE is not allowed if the user does not have write access to
+      this mailbox.
+
+   tag COPY sequence mailbox
+
+      The COPY command copies the specified message(s) to the specified
+      destination mailbox.  If the destination mailbox does not exist,
+      the server should create it.  Before returning an OK to the
+      client, the server should return an unsolicited <n> COPY response
+
+
+
+Crispin                                                        [Page 13]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      for each message copied.  A copy should set the \SEEN flag for all
+      messages that were successfully copied (provided, of course, that
+      the user has write access to this mailbox).
+
+      EXAMPLE:  A003 COPY 2:4 MEETING
+      copies messages 2, 3, and 4 to mailbox "MEETING".
+
+      COPY is not allowed if the user does not have write access to the
+      destination mailbox.
+
+   tag FETCH sequence data
+
+      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 an S-expression list.  The currently defined data items that
+      can be fetched are:
+
+      ALL             Macro equivalent to:
+                      (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE)
+
+      ENVELOPE        The envelope of the message.  The envelope 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.
+                      This may include the following system flags:
+
+                              \RECENT    Message arrived since the
+                                          previous time this mailbox
+                                          was read
+                              \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
+
+      INTERNALDATE    The date and time the message was written to
+                      the mailbox.
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 14]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      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 results.  This is the
+                      concatenation of RFC822.HEADER and RFC822.TEXT.
+
+      RFC822.HEADER   The "raw" RFC 822 format header of the message
+                      as stored on the server.
+
+      RFC822.SIZE     The number of characters 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 as with RFC822 above.
+
+      EXAMPLES:
+
+      A003 FETCH 2:4 ALL
+         fetches the flags, internal date, RFC 822 size, and envelope
+         for messages 2, 3, and 4.
+
+      A004 FETCH 3 RFC822
+         fetches the RFC 822 representation for message 3.
+
+      A005 FETCH 4 (FLAGS RFC822.HEADER)
+         fetches the flags and RFC 822 format header for message 4.
+
+      Note: An attempt to FETCH already-transmitted data may have no
+      result.  See the Implementation Discussion below.
+
+   tag STORE sequence data value
+
+      The STORE command alters data associated with a message in the
+      mailbox.  The currently defined data items that can be stored are:
+
+         FLAGS           Replace the flags for the message with the
+                         argument (in flag list format).
+
+         +FLAGS          Add the flags in the argument to the
+                         message's flag list.
+
+         -FLAGS          Remove the flags in the argument from the
+                         message's flag list.
+
+      STORE is not allowed if the user does not have write access to
+      this mailbox.
+
+
+
+
+Crispin                                                        [Page 15]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      EXAMPLE:  A003 STORE 2:4 +FLAGS (\DELETED)
+      marks messages 2, 3, and 4 for deletion.
+
+   tag SEARCH search_criteria
+
+      The SEARCH command searches the mailbox for messages that match
+      the given set of criteria.  The unsolicited SEARCH <1#number>
+      response from the server is a list of messages that express the
+      intersection (AND function) of all the messages which match that
+      criteria.  For example,
+              A003 SEARCH DELETED FROM "SMITH" SINCE 1-OCT-87
+      returns the message numbers for all deleted messages from Smith
+      that were placed in the mail file since October 1, 1987.
+
+      In all search criteria which use strings, a message matches the
+      criteria if the string is a case-independent substring of that
+      field.  The currently defined criteria are:
+
+      ALL             All messages in the mailbox; the default
+                      initial criterion for ANDing.
+
+      ANSWERED        Messages with the \ANSWERED flag set.
+
+      BCC string      Messages which contain the specified string
+                      in the envelope's BCC field.
+
+      BEFORE date     Messages whose internal date is earlier than
+                      the specified date.
+
+      BODY string     Messages which contain the specified string
+                      in the body of the message.
+
+      CC string       Messages which contain the specified string
+                      in the envelope's CC field.
+
+      DELETED         Messages with the \DELETED flag set.
+
+      FLAGGED         Messages with the \FLAGGED flag set.
+
+      FROM string     Messages which contain the specified string
+                      in the envelope's FROM field.
+
+      KEYWORD flag    Messages with the specified flag set.
+
+      NEW             Messages which have the \RECENT flag set but
+                      not the \SEEN flag.  This is functionally
+                      equivalent to "RECENT UNSEEN".
+
+
+
+
+Crispin                                                        [Page 16]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+      OLD             Messages which do not have the \RECENT flag
+                      set.
+
+      ON date         Messages whose internal date is the same as
+                      the specified date.
+
+      RECENT          Messages which have the \RECENT flag set.
+
+      SEEN            Messages which have the \SEEN flag set.
+
+      SINCE date      Messages whose internal date is later than
+                      the specified date.
+
+      SUBJECT string  Messages which contain the specified string
+                      in the envelope's SUBJECT field.
+
+      TEXT string     Messages which contain the specified string.
+
+      TO string       Messages which contain the specified string in
+                      the envelope's TO field.
+
+      UNANSWERED      Messages which do not have the \ANSWERED flag
+                      set.
+
+      UNDELETED       Messages which do not have the \DELETED flag
+                      set.
+
+      UNFLAGGED       Messages which do not have the \FLAGGED flag
+                      set.
+
+      UNKEYWORD flag  Messages which do not have the specified flag
+                      set.
+
+      UNSEEN          Messages which do not have the \SEEN flag set.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 17]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+Responses
+
+   tag OK text
+
+      This response identifies successful completion of the command with
+      that tag.  The text is a line of human-readable text that may be
+      useful in a protocol telemetry log for debugging purposes.
+
+   tag NO text
+
+      This response identifies unsuccessful completion of the command
+      with that tag.  The text is a line of human-readable text that
+      probably should be displayed to the user in an error report by the
+      client.
+
+   tag BAD text
+
+      This response identifies faulty protocol received from the client;
+      The text is a line of human-readable text that should be recorded
+      in any telemetry as part of a bug report to the maintainer of the
+      client.
+
+   * number message_data
+
+      This response occurs as a result of several different commands.
+      The message_data is one of the following:
+
+      EXISTS  The specified number of messages exists in the mailbox.
+
+      RECENT  The specified number of messages have arrived since the
+              previous time this mailbox was read.
+
+      EXPUNGE The specified message number has been permanently
+              removed from the mailbox, and the next message in the
+              mailbox (if any) becomes that message number.
+
+      STORE data
+              Obsolete and functionally equivalent to FETCH.
+
+      FETCH data
+              This is the principle means by which data about a
+              message is returned to the client.  The data is in a
+              Lisp-like S-expression property list form.  The current
+              properties are:
+
+         ENVELOPE     An S-expression format list that describes the
+                      envelope of a message.  The envelope is computed
+                      by the server by parsing the RFC 822 header into
+
+
+
+Crispin                                                        [Page 18]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+                      the component parts, defaulting various fields
+                      as necessary.
+
+                      The fields of the envelope 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 lists of addresses.
+
+                      An address is an S-expression format list that
+                      describes an electronic mail address.  The fields
+                      of an address are in the following order:
+                      personal name, source-route (a.k.a. the
+                      at-domain-list in SMTP), mailbox name, and
+                      host name.
+
+                      Any field of an envelope or address that is
+                      not applicable is presented as the atom NIL.
+                      Note that the server must default the reply-to
+                      and sender fields from the from field; a client is
+                      not expected to know to do this.
+
+         FLAGS        An S-expression format list of flags that are set
+                      for this message.  This may include the following
+                      system flags:
+
+                      \RECENT       Message arrived since the
+                                     previous time this mailbox
+                                     was read
+                      \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
+
+         INTERNALDATE  A string containing the date and time the
+                       message was written to the mailbox.
+
+         RFC822        A string expressing the message in RFC 822
+                       format.
+
+         RFC822.HEADER A string expressing the RFC 822 format
+                       header of the message
+
+         RFC822.SIZE   A number indicating the number of
+                       characters in the message as expressed
+
+
+
+Crispin                                                        [Page 19]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+                       in RFC 822 format.
+
+         RFC822.TEXT   A string expressing the text body of the
+                       message, omitting the RFC 822 header.
+
+   * FLAGS flag_list
+
+      This response occurs as a result of a SELECT command.  The flag
+      list are the list of flags (at a minimum, the system-defined
+      flags) that are applicable for this mailbox.  Flags other than the
+      system flags are a function of the server implementation.
+
+   * SEARCH number(s)
+
+      This response occurs as a result of a SEARCH command.  The
+      number(s) refer to those messages that match the search criteria.
+      Each number is delimited by a space, e.g., "SEARCH 2 3 6".
+
+   * BBOARD string
+
+      This response occurs as a result of a FIND BBOARDS command.  The
+      string is a bulletin board name that matches the pattern in the
+      command.
+
+   * MAILBOX string
+
+      This response occurs as a result of a FIND MAILBOXES command.  The
+      string is a mailbox name that matches the pattern in the command.
+
+   * BYE text
+
+      This response identifies that the server is about to close the
+      connection.  The text is a line of human-readable text that should
+      be displayed to the user in a status report by the client.  This
+      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
+      servers as an announcement of an inactivity autologout.
+
+   * OK text
+
+      This response identifies normal operation on the server.  No
+      special action by the client is called for, however, the text
+      should be displayed to the user in some fashion.  This is
+      currently only used by servers at startup as a greeting message to
+      show they are ready to accept the first command.
+
+
+
+
+
+
+Crispin                                                        [Page 20]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   * NO text
+
+      This response identifies a warning from the server that does not
+      affect the overall results of any particular request.  The text is
+      a line of human-readable text that should be presented to the user
+      as a warning of improper operation.
+
+   * BAD text
+
+      This response identifies a serious error at the server; it may
+      also indicate faulty protocol from the client in which a tag could
+      not be parsed.  The text is a line of human-readable text that
+      should be presented to the user as a serious or possibly fatal
+      error.  It should also be recorded in any telemetry as part of a
+      bug report to the maintainer of the client and server.
+
+   + text
+
+      This response identifies that the server is ready to accept the
+      text of a literal from the client.  Normally, a command from the
+      client is a single text line.  If the server detects an error in
+      the command, it can simply discard the remainder of the line.  It
+      cannot do this for commands that contain literals, since a literal
+      can be an arbitrarily long amount of text, and the server may not
+      even be expecting a literal.  This mechanism is provided so the
+      client knows not to send a literal until the server expects it,
+      preserving client/server synchronization.
+
+      In practice, this condition is rarely encountered.  In the current
+      protocol, the only client command likely to contain a literal is
+      the LOGIN command.  Consider a server that validates the user
+      before checking the password.  If the password contains "funny"
+      characters and hence is sent as a literal, then if the user is
+      invalid an error would occur before the password is parsed.
+
+      No such synchronization protection is provided for literals sent
+      from the server to the client, for performance reasons.  Any
+      synchronization problems in this direction would be caused by a
+      bug in the client or server.
+
+
+
+
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 21]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+Sample IMAP2 session
+
+   The following is a transcript of an IMAP2 session.  Server output is
+   identified by "S:" and client output by "U:".  In cases where lines
+   are too long to fit within the boundaries of this document, the line
+   is continued on the next line.
+
+   S:   * OK SUMEX-AIM.Stanford.EDU Interim Mail Access Protocol II Service
+         6.1(349) at Thu, 9 Jun 88 14:58:30 PDT
+   U:   a001 login crispin secret
+   S:   a002 OK User CRISPIN logged in at Thu, 9 Jun 88 14:58:42 PDT, job 76
+   U:   a002 select inbox
+   S:   * FLAGS (Bugs SF Party Skating Meeting Flames Request AI Question
+         Note \XXXX \YYYY \Answered \Flagged \Deleted \Seen)
+   S:   * 16 EXISTS
+   S:   * 0 RECENT
+   S:   a002 OK Select complete
+   U:   a003 fetch 16 all
+   S:   * 16 Fetch (Flags (\Seen) InternalDate " 9-Jun-88 12:55:44 PDT"
+         RFC822.Size 637 Envelope ("Sat, 4 Jun 88 13:27:11 PDT"
+         "INFO-MAC Mail Message" (("Larry Fagan" NIL "FAGAN"
+         "SUMEX-AIM.Stanford.EDU")) (("Larry Fagan" NIL "FAGAN"
+         "SUMEX-AIM.Stanford.EDU")) (("Larry Fagan" NIL "FAGAN"
+         "SUMEX-AIM.Stanford.EDU")) ((NIL NIL "rindflEISCH"
+         "SUMEX-AIM.Stanford.EDU")) NIL NIL NIL
+         "<12403828905.13.FAGAN@SUMEX-AIM.Stanford.EDU>"))
+   S:   a003 OK Fetch completed
+   U:   a004 fetch 16 rfc822
+   S:   * 16 Fetch (RFC822 {637}
+   S:   Mail-From: RINDFLEISCH created at  9-Jun-88 12:55:43
+   S:   Mail-From: FAGAN created at  4-Jun-88 13:27:12
+   S:   Date: Sat, 4 Jun 88 13:27:11 PDT
+   S:   From: Larry Fagan  <FAGAN@SUMEX-AIM.Stanford.EDU>
+   S:   To: rindflEISCH@SUMEX-AIM.Stanford.EDU
+   S:   Subject: INFO-MAC Mail Message
+   S:   Message-ID: <12403828905.13.FAGAN@SUMEX-AIM.Stanford.EDU>
+   S:   ReSent-Date: Thu, 9 Jun 88 12:55:43 PDT
+   S:   ReSent-From: TC Rindfleisch <Rindfleisch@SUMEX-AIM.Stanford.EDU>
+   S:   ReSent-To: Yeager@SUMEX-AIM.Stanford.EDU,
+         Crispin@SUMEX-AIM.Stanford.EDU
+   S:   ReSent-Message-ID:
+         <12405133897.80.RINDFLEISCH@SUMEX-AIM.Stanford.EDU>
+   S:
+   S:   The file is <info-mac>usenetv4-55.arc  ...
+   S:   Larry
+   S:   -------
+   S:   )
+   S:   a004 OK Fetch completed
+
+
+
+Crispin                                                        [Page 22]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   U:   a005 logout
+   S:   * BYE DEC-20 IMAP II server terminating connection
+   S:   a005 OK SUMEX-AIM.Stanford.EDU Interim Mail Access Protocol
+         Service logout
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 23]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+Implementation Discussion
+
+   There are several advantages to the scheme of tags and unsolicited
+   responses.  First, the infamous synchronization problems of SMTP and
+   similar protocols do not happen with tagged commands; a command is
+   not considered satisfied until a response with the same tag is seen.
+   Tagging allows an arbitrary amount of other responses ("unsolicited"
+   data) to be sent by the server with no possibility of the client
+   losing synchronization.  Compare this with the problems that FTP or
+   SMTP clients have with continuation, partial completion, and
+   commentary reply codes.
+
+   Another advantage is that a non-lockstep client implementation is
+   possible.  The client could send a command, and entrust the handling
+   of the server responses to a different process that would signal the
+   client when the tagged response comes in.  Under certain
+   circumstances, the client may have more than one command outstanding.
+
+   It was observed that synchronization problems can occur with literals
+   if the literal is not recognized as such.  Fortunately, the cases in
+   which this can happen are rare; a mechanism (the special "+" tag
+   response) was introduced to handle those few cases.  The proper way
+   to address this problem is probably to move towards a record-oriented
+   architecture instead of the text stream model provided by TCP.
+
+   An IMAP2 client must maintain a local cache of data from the mailbox.
+   This cache is an incomplete model of the mailbox, and at startup is
+   empty.  A listener processes all unsolicited data, and updates the
+   cache based on this data.  If a tagged response arrives, the listener
+   unblocks the process that sent the tagged request.
+
+   Unsolicited data needs some discussion.  Unlike most protocols, in
+   which the server merely does the client's bidding, an IMAP2 server
+   has a semi-autonomous role.  By sending "unsolicited data", the
+   server is in effect sending a command to the client -- to update or
+   extend the client's cache with new information from the server.  In
+   other words, a "fetch" command is merely a request to the server to
+   ensure that the client's cache has the most up-to-date version of the
+   requested information.  A server acknowledgement to the "fetch" is a
+   statement that all the requested data has been sent.
+
+   Although no current server does this, a server is not obliged by the
+   protocol to send data that it has already sent and is unchanged.  An
+   exception to this is the actual message text fetching operations
+   (RFC822, RFC822.HEADER, and RFC822.TEXT), owing to the possibly
+   excessive resource consumption of maintaining this data in a cache.
+   It can not be assumed that a FETCH will transmit any data; only that
+   an OK to the FETCH means that the client's cache has the most up-to-
+
+
+
+Crispin                                                        [Page 24]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   date information.
+
+   When a mailbox is selected, the initial unsolicited data from the
+   server arrives.  The first piece of data is the number of messages.
+   By sending a new EXISTS unsolicited data message the server causes
+   the client to resize its cache (this is how newly arrived mail is
+   handled).  If the client attempts to access information from the
+   cache, it will encounter empty spots that will trigger "fetch"
+   requests.  The request would be sent, some unsolicited data including
+   the answer to the fetch will flow back, and then the "fetch" response
+   will unblock the client.
+
+   People familiar with demand-paged virtual memory operating system
+   design will recognize this model as being similar to page-fault
+   handling on a demand-paged system.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 25]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+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 (SP) and not
+   a comma.
+
+   address         ::= "(" addr_name SP addr_adl SP addr_mailbox SP
+                       addr_host ")"
+
+   addr_adl        ::= nil / string
+
+   addr_host       ::= nil / string
+
+   addr_mailbox    ::= nil / string
+
+   addr_name       ::= nil / string
+
+   bboard          ::= "BBOARD" SP string
+
+   check           ::= "CHECK"
+
+   copy            ::= "COPY" SP sequence SP mailbox
+
+   data            ::= ("FLAGS" SP flag_list / "SEARCH" SP 1#number /
+                       "BYE" SP text_line / "OK" SP text_line /
+                       "NO" SP text_line / "BAD" SP text_line)
+
+   date            ::= string in form "dd-mmm-yy hh:mm:ss-zzz"
+
+   envelope        ::= "(" env_date SP env_subject SP env_from SP
+                       env_sender SP env_reply-to SP env_to SP
+                       env_cc SP env_bcc SP env_in-reply-to SP
+                       env_message-id ")"
+
+   env_bcc         ::= nil / "(" 1*address ")"
+
+   env_cc          ::= nil / "(" 1*address ")"
+
+   env_date        ::= string
+
+   env_from        ::= nil / "(" 1*address ")"
+
+   env_in-reply-to ::= nil / string
+
+   env_message-id  ::= nil / string
+
+   env_reply-to    ::= nil / "(" 1*address ")"
+
+
+
+Crispin                                                        [Page 26]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   env_sender      ::= nil / "(" 1*address ")"
+
+   env_subject     ::= nil / string
+
+   env_to          ::= nil / "(" 1*address ")"
+
+   expunge         ::= "EXPUNGE"
+
+   fetch           ::= "FETCH" SP sequence SP ("ALL" / "FAST" /
+                       fetch_att / "(" 1#fetch_att ")")
+
+   fetch_att       ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
+                       "RFC822" / "RFC822.HEADER" / "RFC822.SIZE" /
+                       "RFC822.TEXT"
+
+   find            ::= "FIND" SP find_option SP string
+
+   find_option     ::= "MAILBOXES" / "BBOARDS"
+
+   flag_list       ::= ATOM / "(" 1#ATOM ")"
+
+   literal         ::= "{" NUMBER "}" CRLF ASCII-STRING
+
+   login           ::= "LOGIN" SP userid SP password
+
+   logout          ::= "LOGOUT"
+
+   mailbox         ::= "INBOX" / string
+
+   msg_copy        ::= "COPY"
+
+   msg_data        ::= (msg_exists / msg_recent / msg_expunge /
+                       msg_fetch / msg_copy)
+
+   msg_exists      ::= "EXISTS"
+
+   msg_expunge     ::= "EXPUNGE"
+
+   msg_fetch       ::= ("FETCH" / "STORE") SP "(" 1#("ENVELOPE" SP
+                        envelope / "FLAGS" SP "(" 1#(recent_flag
+                        flag_list) ")" / "INTERNALDATE" SP date /
+                        "RFC822" SP string / "RFC822.HEADER" SP string /
+                        "RFC822.SIZE" SP NUMBER / "RFC822.TEXT" SP
+                        string) ")"
+
+   msg_recent      ::= "RECENT"
+
+   msg_num         ::= NUMBER
+
+
+
+Crispin                                                        [Page 27]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   nil             ::= "NIL"
+
+   noop            ::= "NOOP"
+
+   password        ::= string
+
+   recent_flag     ::= "\RECENT"
+
+   ready           ::= "+" SP text_line
+
+   request         ::= tag SP (noop / login / logout / select / check /
+                       expunge / copy / fetch / store / search / find /
+                       bboard) CRLF
+
+   response        ::= tag SP ("OK" / "NO" / "BAD") SP text_line CRLF
+
+   search          ::= "SEARCH" SP 1#("ALL" / "ANSWERED" /
+                       "BCC" SP string / "BEFORE" SP string /
+                       "BODY" SP string / "CC" SP string / "DELETED" /
+                       "FLAGGED" / "KEYWORD" SP atom / "NEW" / "OLD" /
+                       "ON" SP string / "RECENT" / "SEEN" /
+                       "SINCE" SP string / "TEXT" SP string /
+                       "TO" SP string / "UNANSWERED" / "UNDELETED" /
+                       "UNFLAGGED" / "UNKEYWORD" / "UNSEEN")
+
+   select          ::= "SELECT" SP mailbox
+
+   sequence        ::= NUMBER / (NUMBER "," sequence) / (NUMBER ":"
+                       sequence)
+
+   store           ::= "STORE" SP sequence SP store_att
+
+   store_att       ::= ("+FLAGS" SP flag_list / "-FLAGS" SP flag_list /
+                       "FLAGS" SP flag_list)
+
+   string          ::= atom / """" 1*character """" / literal
+
+   system_flags    ::= "\ANSWERED" SP "\FLAGGED" SP "\DELETED" SP
+                       "\SEEN"
+
+   tag             ::= atom
+
+   unsolicited     ::= "*" SP (msg_num SP msg_data / data) CRLF
+
+   userid          ::= string
+
+
+
+
+
+
+Crispin                                                        [Page 28]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+Implementation Status
+
+   This information is current as of this writing.
+
+   The University of Washington has developed an electronic mail client
+   library called the "C-Client". It provides complete IMAP2, SMTP, and
+   local mailbox (both /usr/spool/mail and mail.txt formats) services in
+   a well-defined way to a user interface main program.  Using the C-
+   Client, the University of Washington has created an operational
+   client for BSD Unix and two operational clients (one basic, one
+   advanced) for the NeXT.
+
+   Stanford University/SUMEX has developed operational IMAP2 clients for
+   Xerox Lisp machines, Texas Instruments Explorers, and the Apple
+   Macintosh.  The core of the Macintosh client is an early version of
+   the C-Client.  SUMEX has also developed IMAP2 servers for TOPS-20 and
+   BSD Unix.
+
+   All of the above software is in production use, with enthusiastic
+   local user communities.  Active development continues on the
+   Macintosh and C-Client based clients and the BSD Unix server.  This
+   software is freely available from the University of Washington and
+   SUMEX.
+
+   IMAP2 software exists for other platforms; for example Nippon
+   Telephone and Telegraph (NTT) has developed an operational IMAP2
+   client for the NTT ELIS.  Several organizations are working on a PC
+   client.
+
+   IMAP2 can be used to access mailboxes at very remote sites, where
+   echo delays and frequent outages make TELNET and running a local mail
+   reader intolerable.  For example, from a desktop workstation on the
+   University of Washington local network the author routinely uses
+   IMAP2 to read and manage mailboxes on various University of
+   Washington local servers, at two systems at Stanford University, at a
+   Milnet site, and at a site in Tokyo, Japan.
+
+   This specification does not make any formal definition of size
+   restrictions, but the DEC-20 server has the following limitations:
+
+    . length of a mailbox: 7,077,888 characters
+    . maximum number of messages: 18,432 messages
+    . length of a command line: 10,000 characters
+    . length of the local host name: 64 characters
+    . length of a "short" argument: 39 characters
+    . length of a "long" argument: 491,520 characters
+    . maximum amount of data output in a single fetch:
+      655,360 characters
+
+
+
+Crispin                                                        [Page 29]
+
+RFC 1176                         IMAP2                       August 1990
+
+
+   To date, nobody has run up against any of these limitations, many of
+   which are substantially larger than most current user mail reading
+   programs.
+
+Acknowledgements
+
+   Bill Yeager and Rich Acuff both contributed invaluable suggestions in
+   the evolution of IMAP2 from the original IMAP.  James Rice pointed
+   out several ambiguities in the previous IMAP2 specification and
+   otherwise would not allow me to leave bad enough along.  Laurence
+   Lundblade reviewed a draft of this version and made several helpful
+   suggestions.
+
+   Many dedicated individuals have worked on IMAP2 software, including:
+   Mark Crispin, Frank Gilmurray, Christopher Lane, Hiroshi Okuno,
+   Christopher Schmidt, and Bill Yeager.
+
+   Any mistakes, flaws, or sins of omission in this IMAP2 protocol
+   specification are, however, strictly my own; and the mention of any
+   name above does not imply an endorsement.
+
+Security Considerations
+
+   Security issues are not discussed in this memo.
+
+Author's Address
+
+   Mark R. Crispin
+   Panda Programming
+   6158 Lariat Loop NE
+   Bainbridge Island, WA 98110-2020
+
+   Phone: (206) 842-2385
+
+   EMail: mrc@Tomobiki-Cho.CAC.Washington.EDU
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Crispin                                                        [Page 30]
+
\ No newline at end of file