Network Working Group                                           J. Myers
Request for Comments: 2359                       Netscape Communications
Category: Standards Track                                      June 1998


                        IMAP4 UIDPLUS extension

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

IESG NOTE

   The IMAP extension described here assumes a particular means of using
   IMAP to support disconnected operation.  However, this means of
   supporting disconnected operation is not yet documented.  Also, there
   are multiple theories about how best to do disconnected operation in
   IMAP, and as yet, there is no consensus on which one should be
   adopted as a standard.

   This document is being approved as a Proposed Standard because it
   does not appear to have technical flaws in itelf.  However, approval
   of this document as a Proposed Standard should not be considered an
   IETF endorsement of any particular means of doing disconnected
   operation in IMAP.

Table of Contents

   1.   Abstract ..............................................    2
   2.   Conventions Used in this Document .....................    2
   3.   Introduction and Overview .............................    2
   4.   Features ..............................................    2
   4.1. UID EXPUNGE Command ...................................    2
   4.2. APPENDUID response code ...............................    3
   4.3. COPYUID response code .................................    4
   5.   Formal Syntax .........................................    4
   6.   References ............................................    4
   7.   Security Considerations ...............................    5
   8.   Author's Address ......................................    5
   9.   Full Copyright Statement ..............................    6

1.   Abstract

   The UIDPLUS extension of the Internet Message Access Protocol [IMAP4]
   provides a set of features intended to reduce the amount of time and
   resources used by some client operations.  The features in UIDPLUS
   are primarily intended for disconnected-use clients.

2.   Conventions Used in this Document

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

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [KEYWORDS].

3.   Introduction and Overview

   The UIDPLUS extension is present in any IMAP4 server implementation
   which returns "UIDPLUS" as one of the supported capabilities to the
   CAPABILITY command.  The UIDPLUS extension contains one additional
   command and additional data returned with successful APPEND and COPY
   commands.

   Clients that wish to use the new command in UIDPLUS must of course
   first test for the presence of the extension by issuing a CAPABILITY
   command.  Each of the features in UIDPLUS are optimizations; clients
   can provide the same functionality, albeit more slowly, by using
   commands in the base protocol.  With each feature, this document
   recommends a fallback approach to take when the UIDPLUS extension is
   not supported by the server.

4.   Features

4.1. UID EXPUNGE Command

   Arguments:  message set

   Data:       untagged responses: EXPUNGE

   Result:     OK - expunge completed
               NO - expunge failure (e.g. permission denied)
               BAD - command unknown or arguments invalid

      The UID EXPUNGE command permanently removes from the currently
      selected mailbox all messages that both have the \Deleted flag set
      and have a UID that is included in the specified message set.  If
      a message either does not have the \Deleted flag set or is has a
      UID that is not included in the specified message set, it is not
      affected.

      This command may be used to ensure that a replayed EXPUNGE command
      does not remove any messages that have been marked as \Deleted
      between the time that the user requested the expunge operation and
      the time the server processes the command.

      If the server does not support the UIDPLUS capability, the client
      should fall back to using the STORE command to temporarily remove
      the \Deleted flag from messages it does not want to remove.  The
      client could alternatively fall back to using the EXPUNGE command,
      risking the unintended removal of some messages.

   Example:    C: A003 UID EXPUNGE 3000:3002
               S: * 3 EXPUNGE
               S: * 3 EXPUNGE
               S: * 3 EXPUNGE
               S: A003 OK UID EXPUNGE completed

4.2. APPENDUID response code

   Successful APPEND commands return an APPENDUID response code in the
   tagged OK response.  The APPENDUID response code contains as
   arguments the UIDVALIDITY of the destination mailbox and the UID
   assigned to the appended message.

   If the server does not support the UIDPLUS capability, the client can
   only discover this information by selecting the destination mailbox
   and issuing FETCH commands.

   Example:    C: A003 APPEND saved-messages (\Seen) {310}
               C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
               C: From: Fred Foobar <foobar@Blurdybloop.COM>
               C: Subject: afternoon meeting
               C: To: mooch@owatagu.siam.edu
               C: Message-Id: <B27397-0100000@Blurdybloop.COM>
               C: MIME-Version: 1.0
               C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
               C:
               C: Hello Joe, do you think we can meet at 3:30 tomorrow?
               C:
               S: A003 OK [APPENDUID 38505 3955] APPEND completed

4.3. COPYUID response code

   Successful COPY and UID COPY commands return a COPYUID response code
   in the tagged OK response whenever at least one message was copied.
   The COPYUID response code contains as an argument the UIDVALIDITY of
   the appended-to mailbox, a message set containing the UIDs of the
   messages copied to the destination mailbox, in the order they were
   copied, and a message containing the UIDs assigned to the copied
   messages, in the order they were assigned.  Neither of the message
   sets may contain extraneous UIDs or the symbol '*'.

   If the server does not support the UIDPLUS capability, the client can
   only discover this information by selecting the destination mailbox
   and issuing FETCH commands.

   Example:    C: A003 COPY 2:4 MEETING
               S: A003 OK [COPYUID 38505 304,319:320 3956:3958] Done
               C: A003 UID COPY 305:310 MEETING
               S: A003 OK Done

5.   Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4].
   Non-terminals referenced but not defined below are as defined by
   [IMAP4].

   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.

   resp_code_apnd  ::= "APPENDUID" SPACE nz_number SPACE uniqueid

   resp_code_copy  ::= "COPYUID" SPACE nz_number SPACE set SPACE set

   uid_expunge     ::= "UID" SPACE "EXPUNGE" SPACE set

6.   References

   [IMAP4]    Crispin, M., "Internet Message Access Protocol -
              Version 4rev1", RFC 2060, December 1996.

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

7.   Security Considerations

   There are no known security issues with this extension.

8.   Author's Address

   John Gardiner Myers
   Netscape Communications
   501 East Middlefield Road
   Mail Stop MV-029
   Mountain View, CA  94043

   EMail: jgmyers@netscape.com

9.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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