Internet Message Access Protocol (IMAP) - UIDPLUS extension
draft-crispin-imap-rfc2359bis-04

Network Working Group                                         M. Crispin
INTERNET DRAFT: IMAP UIDPLUS extension                          May 2005
Obsoletes: 2359
Document: internet-drafts/draft-crispin-imap-rfc2359bis-04.txt

      Internet Message Access Protocol (IMAP) - UIDPLUS extension

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Abstract

    The UIDPLUS extension of the Internet Message Access Protocol [IMAP]
    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.

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", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are
    to be interpreted as described in [KEYWORDS].

    A "UID set" is similar to the [IMAP] sequence set; however, the "*"
    value for sequence number is not permitted.

Introduction and Overview

    The UIDPLUS extension is present in any IMAP server implementation
    which returns "UIDPLUS" as one of the supported capabilities to the
    CAPABILITY command.

    The UIDPLUS extension defines an additional command.  In addition,
    this document recommends new status response codes in IMAP which
    SHOULD be returned by all server implementations, regardless of
    whether or not the UIDPLUS extension is implemented.

    The added facilities of the features in UIDPLUS are optimizations;
    clients can provide equivalent functionality, albeit less
    efficiently, by using facilities in the base protocol.

1. Additional Commands

    The following command definition is an extension to [IMAP] section
    6.4.

1.1 UID EXPUNGE Command

    Arguments:  sequence 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 sequence set.  If
       a message either does not have the \Deleted flag set or has a UID
       that is not included in the specified sequence 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

2. Additional Response Codes

    The following response codes are extensions to the response codes
    defined in [IMAP] section 7.1.  With limited exceptions, discussed
    below, server implementations that advertise the UIDPLUS extension
    SHOULD return these response codes.

    In the case of a mailbox which has permissions set so that the client
    can COPY or APPEND to the mailbox, but not SELECT or EXAMINE it, the
    server SHOULD NOT send an APPENDUID or COPYUID response code as it
    would disclose information about the mailbox.

    In the case of a mailbox that has UIDNOTSTICKY status (as defined
    below), the server MAY omit the APPENDUID or COPYUID response code as
    it is not meaningful.

    If the server does not return the APPENDUID or COPYUID response
    codes, the client can discover this information by selecting the
    destination mailbox.  The location of messages placed in the
    destination mailbox by COPY or APPEND can be determined by using
    FETCH and/or SEARCH commands (e.g. for Message-ID or some unique
    marker placed in the message in an APPEND).

    APPENDUID

       Followed by the UIDVALIDITY of the destination mailbox and the
       UID assigned to the appended message in the destination mailbox,
       indicates that the message has been appended to the destination
       mailbox with that UID.

       If the server also supports the [MULTIAPPEND] extension, and if
       multiple messages were appended in the APPEND command, then the
       second value is a UID set containing the UIDs assigned to
       the appended messages, in the order they were transmitted in the
       APPEND command.  This UID set may not contain extraneous
       UIDs or the symbol "*".

          Note: the UID set form of the APPENDUID response code MUST
          NOT be used if only a single message was appended.  In
          particular, a server MUST NOT send a range such as 123:123.
          This is because a client which does not support [MULTIAPPEND]
          expects only a single UID and not a UID set.

       UIDs are assigned strictly ascending in the mailbox (refer to
       [IMAP], section 2.3.1.1) and UID ranges are as in [IMAP]; in
       particular, note that a range of 12:10 is exactly equivalent to
       10:12 and refers to the sequence 10,11,12.

       This response code is returned in a tagged OK response to the
       APPEND command.

    COPYUID

       Followed by the UIDVALIDITY of the destination mailbox, a UID
       set containing the UIDs of the message(s) in the source mailbox
       which were copied to the destination mailbox, and a UID set
       containing the UIDs assigned to the copied message(s) in the
       destination mailbox, indicates that the message(s) have been
       copied to the destination mailbox with the stated UID(s).

       The source UID set is in the order the message(s) were copied; the
       destination UID set corresponds to the source UID set and is in
       the same order.  Neither of the UID sets may contain extraneous
       UIDs or the symbol "*".

       UIDs are assigned strictly ascending in the mailbox (refer to
       [IMAP], section 2.3.1.1) and UID ranges are as in [IMAP]; in
       particular, note that a range of 12:10 is exactly equivalent to
       10:12 and refers to the sequence 10,11,12.

       This response code is returned in a tagged OK response to the
       COPY command.

    UIDNOTSTICKY

       The selected mailbox is supported by a mail store which does not
       support persistent UIDs; that is, UIDVALIDITY will be different
       each time the mailbox is selected.  Consequently, APPEND or COPY
       to this mailbox will not return an APPENDUID or COPYUID response
       code.

       This response code is returned in an untagged NO response to the
       SELECT command.

          Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores.
          This facility exists to support legacy mail stores in which
          it is technically infeasible to support persistant UIDs.
          This should be avoided when designing new mail stores.

    Example:    C: A003 APPEND saved-messages (\Seen) {297}
                C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
                C: From: Fred Foobar <foobar@example.com>
                C: Subject: afternoon meeting
                C: To: mooch@example.com
                C: Message-Id: <B27397-0100000@example.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
                C: A004 COPY 2:4 meeting
                S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done
                C: A005 UID COPY 305:310 meeting
                S: A005 OK No matching messages, so nothing copied
                C: A006 COPY 2 funny
                S: A006 OK Done
                C: A007 SELECT funny
                S: * 1 EXISTS
                S: * 1 RECENT
                S: * OK [UNSEEN 1] Message 1 is first unseen
                S: * OK [UIDVALIDITY 3857529045] Validity session-only
                S: * OK [UIDNEXT 2] Predicted next UID
                S: * NO [UIDNOTSTICKY] Non-persistent UIDs
                S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
                S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited
                S: A007 OK [READ-WRITE] SELECT completed

    In this example, A003 and A004 demonstrate successful appending and
    copying to a mailbox which returns the UIDs assigned to the messages.
    A005 is an example in which no messages were copied; this is because
    in A003 we see that message 2 had UID 304 and message 3 had UID 319;
    therefore UIDs 305 through 310 do not exist (refer to section 2.3.1.1
    of [IMAP] for further explanation).  A006 is an example of a message
    being copied that did not return a COPYUID; and as expected A007
    shows that the mail store containing that mailbox does not support
    persistent UIDs.

5.   Formal Syntax

    Formal syntax is defined using ABNF [ABNF], extending the ABNF rules
    defined in [IMAP4].  The IMAP4 ABNF should be imported first before
    attempting to validate these rules.

    append-uid      = uniqueid

    capability      =/ "UIDPLUS"

    command-select  =/ uid-expunge

    resp-code-apnd  = "APPENDUID" SP nz-number SP append-uid

    resp-code-copy  = "COPYUID" SP nz-number SP uid-set SP uid-set

    resp-text-code  =/ resp-code-apnd / resp-code-copy / "UIDNOTSTICKY"
                      ; incorporated before the expansion rule of
                      ;  atom [SP 1*<any TEXT-CHAR except "]">]
                      ; which appears in [IMAP]

    uid-expunge     = "UID" SP "EXPUNGE" SP sequence-set

    uid-set         = (uniqueid / uid-range) *("," uid-set)

    uid-range       = (uniqueid ":" uniqueid)
                      ; two uniqueid values and all values
                      ; between these two regards of order.
                      ; Example: 2:4 and 4:2 are equivalent.

    Servers which support [MULTIAPPEND] will have the following extension
    to the above rules:

    append-uid      =/ uid-set
                      ; only permitted if client uses [MULTIAPPEND]
                      ; to append multiple messages.

Security Considerations

    The COPYUID and APPENDUID response codes return information about the
    mailbox.  These response codes SHOULD NOT be issused if the client
    does not have access to SELECT or EXAMINE the mailbox.

IANA Considerations

    This document constitutes registration of the UIDPLUS capability in
    the imap4-capabilities registry, replacing RFC 2359.

Normative References

    [ABNF]        Crocker, D. and P. Overell, "Augmented BNF for Syntax
                  Specifications: ABNF", RFC 2234, November 1997.

    [IMAP]        Crispin, M., "Internet Message Access Protocol -
                  Version 4rev1", RFC 3501, March 2003.

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

    [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) -
                  MULTIAPPEND Extension", RFC 3502, March 2003.

    [RFC-2822]    Resnick, P., "Internet Message Format", RFC 2822, April
                  2001.

Informative References

    [RFC-2359]    Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June
                  1988.

Acknowledgements

    This document obsoletes [RFC-2359].  However, it is based upon that
    document, and takes substantial text from it.

Author's Address

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

    Phone: (206) 543-5762
    EMail: MRC@CAC.Washington.EDU

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    patent or other IPR claims of which I am aware have been disclosed,
    and any of which I become aware will be disclosed, in accordance with
    RFC 3668.

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