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Network Working Group                                         M. CrispinRequest for Comments: 4315                                 December 2005Obsoletes:2359Category: Standards TrackInternet Message Access Protocol (IMAP) - UIDPLUS extensionStatus 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 (2005).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.1.  Introduction and Overview   The UIDPLUS extension is present in any IMAP server implementation   that 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 that   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.1.1.  Conventions Used in This Document   In examples, "C:" and "S:" indicate lines sent by the client and   server, respectively.Crispin                     Standards Track                     [Page 1]

RFC 4315                IMAP - UIDPLUS Extension           December 2005   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 a sequence number is not permitted.2.  Additional Commands   The following command definition is an extension to [IMAP]section6.4.2.1.  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 all messages that both      have the \Deleted flag set and have a UID that is included in the      specified sequence set from the currently selected mailbox.  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 is particularly useful for disconnected use clients.      By using UID EXPUNGE instead of EXPUNGE when resynchronizing with      the server, the client can ensure that it does not inadvertantly      remove any messages that have been marked as \Deleted by other      clients between the time that the client was last connected and      the time the client resynchronizes.      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, then      issuing the EXPUNGE command.  Finally, the client should use the      STORE command to restore the \Deleted flag on the messages in      which it was temporarily removed.      Alternatively, the client may fall back to using just the EXPUNGE      command, risking the unintended removal of some messages.Crispin                     Standards Track                     [Page 2]

RFC 4315                IMAP - UIDPLUS Extension           December 2005   Example:    C: A003 UID EXPUNGE 3000:3002               S: * 3 EXPUNGE               S: * 3 EXPUNGE               S: * 3 EXPUNGE               S: A003 OK UID EXPUNGE completed3.  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 that 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 that does not support [MULTIAPPEND] expects         only a single UID and not a UID set.Crispin                     Standards Track                     [Page 3]

RFC 4315                IMAP - UIDPLUS Extension           December 2005      UIDs are assigned in strictly ascending order 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 that      were copied to the destination mailbox and 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 in strictly ascending order 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 that 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 persistent UIDs.  This         should be avoided when designing new mail stores.Crispin                     Standards Track                     [Page 4]

RFC 4315                IMAP - UIDPLUS Extension           December 2005   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 that 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 tosection2.3.1.1 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.4.  Formal Syntax   Formal syntax is defined using ABNF [ABNF], which extends the ABNF   rules defined in [IMAP].  The IMAP4 ABNF should be imported before   attempting to validate these rules.   append-uid      = uniqueid   capability      =/ "UIDPLUS"Crispin                     Standards Track                     [Page 5]

RFC 4315                IMAP - UIDPLUS Extension           December 2005   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 "]">]                     ; that 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 that 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.5.  Security Considerations   The COPYUID and APPENDUID response codes return information about the   mailbox, which may be considered sensitive if the mailbox has   permissions set that permit the client to COPY or APPEND to the   mailbox, but not SELECT or EXAMINE it.   Consequently, these response codes SHOULD NOT be issued if the client   does not have access to SELECT or EXAMINE the mailbox.6.  IANA Considerations   This document constitutes registration of the UIDPLUS capability in   the imap4-capabilities registry, replacing [RFC2359].7.  Normative References   [ABNF]        Crocker, D. and P. Overell, "Augmented BNF for Syntax                 Specifications: ABNF",RFC 4234, October 2005.Crispin                     Standards Track                     [Page 6]

RFC 4315                IMAP - UIDPLUS Extension           December 2005   [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 2003.8.  Informative References   [RFC2359]     Myers, J., "IMAP4 UIDPLUS extension",RFC 2359, June                 1998.9.  Changes fromRFC 2359   This document obsoletes [RFC2359].  However, it is based upon that   document, and takes substantial text from it (albeit with numerous   clarifications in wording).   [RFC2359] implied that a server must always return COPYUID/APPENDUID   data; thus suggesting that in such cases the server should return   arbitrary data if the destination mailbox did not support persistent   UIDs.  This document adds the UIDNOTSTICKY response code to indicate   that a mailbox does not support persistent UIDs, and stipulates that   a UIDPLUS server does not return COPYUID/APPENDUID data when the COPY   (or APPEND) destination mailbox has UIDNOTSTICKY status.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.EDUCrispin                     Standards Track                     [Page 7]

RFC 4315                IMAP - UIDPLUS Extension           December 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Crispin                     Standards Track                     [Page 8]