RFC2359 - IMAP4 UIDPLUS extension

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　　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", RFC2060, December 1996.

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.

[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet
Text Messages", STD 11, RFC822, 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
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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