452 lines
16 KiB
Plaintext
452 lines
16 KiB
Plaintext
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Network Working Group M. Crispin
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Request for Comments: 4315 December 2005
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Obsoletes: 2359
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Category: Standards Track
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Internet Message Access Protocol (IMAP) - UIDPLUS extension
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Status of This Memo
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This document specifies an Internet standards track protocol for the
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Internet community, and requests discussion and suggestions for
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improvements. Please refer to the current edition of the "Internet
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Official Protocol Standards" (STD 1) for the standardization state
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and status of this protocol. Distribution of this memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (2005).
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Abstract
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The UIDPLUS extension of the Internet Message Access Protocol (IMAP)
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provides a set of features intended to reduce the amount of time and
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resources used by some client operations. The features in UIDPLUS
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are primarily intended for disconnected-use clients.
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1. Introduction and Overview
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The UIDPLUS extension is present in any IMAP server implementation
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that returns "UIDPLUS" as one of the supported capabilities to the
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CAPABILITY command.
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The UIDPLUS extension defines an additional command. In addition,
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this document recommends new status response codes in IMAP that
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SHOULD be returned by all server implementations, regardless of
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whether or not the UIDPLUS extension is implemented.
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The added facilities of the features in UIDPLUS are optimizations;
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clients can provide equivalent functionality, albeit less
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efficiently, by using facilities in the base protocol.
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1.1. Conventions Used in This Document
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In examples, "C:" and "S:" indicate lines sent by the client and
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server, respectively.
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Crispin Standards Track [Page 1]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
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be interpreted as described in [KEYWORDS].
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A "UID set" is similar to the [IMAP] sequence set; however, the "*"
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value for a sequence number is not permitted.
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2. Additional Commands
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The following command definition is an extension to [IMAP] section
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6.4.
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2.1. UID EXPUNGE Command
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Arguments: sequence set
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Data: untagged responses: EXPUNGE
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Result: OK - expunge completed
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NO - expunge failure (e.g., permission denied)
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BAD - command unknown or arguments invalid
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The UID EXPUNGE command permanently removes all messages that both
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have the \Deleted flag set and have a UID that is included in the
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specified sequence set from the currently selected mailbox. If a
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message either does not have the \Deleted flag set or has a UID
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that is not included in the specified sequence set, it is not
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affected.
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This command is particularly useful for disconnected use clients.
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By using UID EXPUNGE instead of EXPUNGE when resynchronizing with
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the server, the client can ensure that it does not inadvertantly
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remove any messages that have been marked as \Deleted by other
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clients between the time that the client was last connected and
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the time the client resynchronizes.
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If the server does not support the UIDPLUS capability, the client
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should fall back to using the STORE command to temporarily remove
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the \Deleted flag from messages it does not want to remove, then
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issuing the EXPUNGE command. Finally, the client should use the
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STORE command to restore the \Deleted flag on the messages in
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which it was temporarily removed.
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Alternatively, the client may fall back to using just the EXPUNGE
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command, risking the unintended removal of some messages.
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Crispin Standards Track [Page 2]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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Example: C: A003 UID EXPUNGE 3000:3002
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S: * 3 EXPUNGE
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S: * 3 EXPUNGE
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S: * 3 EXPUNGE
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S: A003 OK UID EXPUNGE completed
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3. Additional Response Codes
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The following response codes are extensions to the response codes
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defined in [IMAP] section 7.1. With limited exceptions, discussed
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below, server implementations that advertise the UIDPLUS extension
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SHOULD return these response codes.
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In the case of a mailbox that has permissions set so that the client
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can COPY or APPEND to the mailbox, but not SELECT or EXAMINE it, the
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server SHOULD NOT send an APPENDUID or COPYUID response code as it
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would disclose information about the mailbox.
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In the case of a mailbox that has UIDNOTSTICKY status (as defined
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below), the server MAY omit the APPENDUID or COPYUID response code as
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it is not meaningful.
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If the server does not return the APPENDUID or COPYUID response
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codes, the client can discover this information by selecting the
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destination mailbox. The location of messages placed in the
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destination mailbox by COPY or APPEND can be determined by using
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FETCH and/or SEARCH commands (e.g., for Message-ID or some unique
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marker placed in the message in an APPEND).
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APPENDUID
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Followed by the UIDVALIDITY of the destination mailbox and the UID
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assigned to the appended message in the destination mailbox,
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indicates that the message has been appended to the destination
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mailbox with that UID.
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If the server also supports the [MULTIAPPEND] extension, and if
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multiple messages were appended in the APPEND command, then the
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second value is a UID set containing the UIDs assigned to the
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appended messages, in the order they were transmitted in the
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APPEND command. This UID set may not contain extraneous UIDs or
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the symbol "*".
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Note: the UID set form of the APPENDUID response code MUST NOT
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be used if only a single message was appended. In particular,
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a server MUST NOT send a range such as 123:123. This is
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because a client that does not support [MULTIAPPEND] expects
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only a single UID and not a UID set.
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Crispin Standards Track [Page 3]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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UIDs are assigned in strictly ascending order in the mailbox
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(refer to [IMAP], section 2.3.1.1) and UID ranges are as in
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[IMAP]; in particular, note that a range of 12:10 is exactly
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equivalent to 10:12 and refers to the sequence 10,11,12.
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This response code is returned in a tagged OK response to the
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APPEND command.
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COPYUID
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Followed by the UIDVALIDITY of the destination mailbox, a UID set
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containing the UIDs of the message(s) in the source mailbox that
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were copied to the destination mailbox and containing the UIDs
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assigned to the copied message(s) in the destination mailbox,
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indicates that the message(s) have been copied to the destination
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mailbox with the stated UID(s).
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The source UID set is in the order the message(s) were copied; the
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destination UID set corresponds to the source UID set and is in
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the same order. Neither of the UID sets may contain extraneous
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UIDs or the symbol "*".
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UIDs are assigned in strictly ascending order in the mailbox
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(refer to [IMAP], section 2.3.1.1) and UID ranges are as in
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[IMAP]; in particular, note that a range of 12:10 is exactly
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equivalent to 10:12 and refers to the sequence 10,11,12.
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This response code is returned in a tagged OK response to the COPY
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command.
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UIDNOTSTICKY
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The selected mailbox is supported by a mail store that does not
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support persistent UIDs; that is, UIDVALIDITY will be different
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each time the mailbox is selected. Consequently, APPEND or COPY
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to this mailbox will not return an APPENDUID or COPYUID response
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code.
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This response code is returned in an untagged NO response to the
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SELECT command.
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Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores.
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This facility exists to support legacy mail stores in which it
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is technically infeasible to support persistent UIDs. This
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should be avoided when designing new mail stores.
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Crispin Standards Track [Page 4]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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Example: C: A003 APPEND saved-messages (\Seen) {297}
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C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
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C: From: Fred Foobar <foobar@example.com>
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C: Subject: afternoon meeting
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C: To: mooch@example.com
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C: Message-Id: <B27397-0100000@example.com>
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C: MIME-Version: 1.0
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C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
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C:
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C: Hello Joe, do you think we can meet at 3:30 tomorrow?
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C:
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S: A003 OK [APPENDUID 38505 3955] APPEND completed
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C: A004 COPY 2:4 meeting
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S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done
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C: A005 UID COPY 305:310 meeting
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S: A005 OK No matching messages, so nothing copied
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C: A006 COPY 2 funny
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S: A006 OK Done
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C: A007 SELECT funny
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S: * 1 EXISTS
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S: * 1 RECENT
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S: * OK [UNSEEN 1] Message 1 is first unseen
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S: * OK [UIDVALIDITY 3857529045] Validity session-only
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S: * OK [UIDNEXT 2] Predicted next UID
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S: * NO [UIDNOTSTICKY] Non-persistent UIDs
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S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
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S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited
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S: A007 OK [READ-WRITE] SELECT completed
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In this example, A003 and A004 demonstrate successful appending and
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copying to a mailbox that returns the UIDs assigned to the messages.
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A005 is an example in which no messages were copied; this is because
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in A003, we see that message 2 had UID 304, and message 3 had UID
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319; therefore, UIDs 305 through 310 do not exist (refer to section
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2.3.1.1 of [IMAP] for further explanation). A006 is an example of a
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message being copied that did not return a COPYUID; and, as expected,
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A007 shows that the mail store containing that mailbox does not
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support persistent UIDs.
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4. Formal Syntax
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Formal syntax is defined using ABNF [ABNF], which extends the ABNF
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rules defined in [IMAP]. The IMAP4 ABNF should be imported before
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attempting to validate these rules.
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append-uid = uniqueid
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capability =/ "UIDPLUS"
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Crispin Standards Track [Page 5]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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command-select =/ uid-expunge
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resp-code-apnd = "APPENDUID" SP nz-number SP append-uid
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resp-code-copy = "COPYUID" SP nz-number SP uid-set SP uid-set
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resp-text-code =/ resp-code-apnd / resp-code-copy / "UIDNOTSTICKY"
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; incorporated before the expansion rule of
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; atom [SP 1*<any TEXT-CHAR except "]">]
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; that appears in [IMAP]
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uid-expunge = "UID" SP "EXPUNGE" SP sequence-set
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uid-set = (uniqueid / uid-range) *("," uid-set)
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uid-range = (uniqueid ":" uniqueid)
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; two uniqueid values and all values
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; between these two regards of order.
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; Example: 2:4 and 4:2 are equivalent.
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Servers that support [MULTIAPPEND] will have the following extension
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to the above rules:
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append-uid =/ uid-set
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; only permitted if client uses [MULTIAPPEND]
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; to append multiple messages.
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5. Security Considerations
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The COPYUID and APPENDUID response codes return information about the
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mailbox, which may be considered sensitive if the mailbox has
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permissions set that permit the client to COPY or APPEND to the
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mailbox, but not SELECT or EXAMINE it.
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Consequently, these response codes SHOULD NOT be issued if the client
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does not have access to SELECT or EXAMINE the mailbox.
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6. IANA Considerations
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This document constitutes registration of the UIDPLUS capability in
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the imap4-capabilities registry, replacing [RFC2359].
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7. Normative References
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[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
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Specifications: ABNF", RFC 4234, October 2005.
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Crispin Standards Track [Page 6]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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[IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
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VERSION 4rev1", RFC 3501, March 2003.
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[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
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[MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) -
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MULTIAPPEND Extension", RFC 3502, March 2003.
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8. Informative References
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[RFC2359] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June
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1998.
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9. Changes from RFC 2359
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This document obsoletes [RFC2359]. However, it is based upon that
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document, and takes substantial text from it (albeit with numerous
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clarifications in wording).
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[RFC2359] implied that a server must always return COPYUID/APPENDUID
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data; thus suggesting that in such cases the server should return
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arbitrary data if the destination mailbox did not support persistent
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UIDs. This document adds the UIDNOTSTICKY response code to indicate
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that a mailbox does not support persistent UIDs, and stipulates that
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a UIDPLUS server does not return COPYUID/APPENDUID data when the COPY
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(or APPEND) destination mailbox has UIDNOTSTICKY status.
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Author's Address
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Mark R. Crispin
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Networks and Distributed Computing
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University of Washington
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4545 15th Avenue NE
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Seattle, WA 98105-4527
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Phone: (206) 543-5762
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EMail: MRC@CAC.Washington.EDU
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Crispin Standards Track [Page 7]
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RFC 4315 IMAP - UIDPLUS Extension December 2005
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Full Copyright Statement
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Copyright (C) The Internet Society (2005).
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This document is subject to the rights, licenses and restrictions
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contained in BCP 78, and except as set forth therein, the authors
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retain all their rights.
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This document and the information contained herein are provided on an
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"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
|
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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Intellectual Property
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The IETF takes no position regarding the validity or scope of any
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Intellectual Property Rights or other rights that might be claimed to
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pertain to the implementation or use of the technology described in
|
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this document or the extent to which any license under such rights
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might or might not be available; nor does it represent that it has
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made any independent effort to identify any such rights. Information
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on the procedures with respect to rights in RFC documents can be
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found in BCP 78 and BCP 79.
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Copies of IPR disclosures made to the IETF Secretariat and any
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assurances of licenses to be made available, or the result of an
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attempt made to obtain a general license or permission for the use of
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such proprietary rights by implementers or users of this
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specification can be obtained from the IETF on-line IPR repository at
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http://www.ietf.org/ipr.
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The IETF invites any interested party to bring to its attention any
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||
copyrights, patents or patent applications, or other proprietary
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||
rights that may cover technology that may be required to implement
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||
this standard. Please address the information to the IETF at ietf-
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ipr@ietf.org.
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|
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Acknowledgement
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||
|
||
Funding for the RFC Editor function is currently provided by the
|
||
Internet Society.
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Crispin Standards Track [Page 8]
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