7Network Working Group M. Crispin
8Request for Comments: 4315 December 2005
10Category: Standards Track
13 Internet Message Access Protocol (IMAP) - UIDPLUS extension
17 This document specifies an Internet standards track protocol for the
18 Internet community, and requests discussion and suggestions for
19 improvements. Please refer to the current edition of the "Internet
20 Official Protocol Standards" (STD 1) for the standardization state
21 and status of this protocol. Distribution of this memo is unlimited.
25 Copyright (C) The Internet Society (2005).
29 The UIDPLUS extension of the Internet Message Access Protocol (IMAP)
30 provides a set of features intended to reduce the amount of time and
31 resources used by some client operations. The features in UIDPLUS
32 are primarily intended for disconnected-use clients.
341. Introduction and Overview
36 The UIDPLUS extension is present in any IMAP server implementation
37 that returns "UIDPLUS" as one of the supported capabilities to the
40 The UIDPLUS extension defines an additional command. In addition,
41 this document recommends new status response codes in IMAP that
42 SHOULD be returned by all server implementations, regardless of
43 whether or not the UIDPLUS extension is implemented.
45 The added facilities of the features in UIDPLUS are optimizations;
46 clients can provide equivalent functionality, albeit less
47 efficiently, by using facilities in the base protocol.
491.1. Conventions Used in This Document
51 In examples, "C:" and "S:" indicate lines sent by the client and
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60RFC 4315 IMAP - UIDPLUS Extension December 2005
63 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
64 "SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
65 be interpreted as described in [KEYWORDS].
67 A "UID set" is similar to the [IMAP] sequence set; however, the "*"
68 value for a sequence number is not permitted.
72 The following command definition is an extension to [IMAP] section
77 Arguments: sequence set
79 Data: untagged responses: EXPUNGE
81 Result: OK - expunge completed
82 NO - expunge failure (e.g., permission denied)
83 BAD - command unknown or arguments invalid
85 The UID EXPUNGE command permanently removes all messages that both
86 have the \Deleted flag set and have a UID that is included in the
87 specified sequence set from the currently selected mailbox. If a
88 message either does not have the \Deleted flag set or has a UID
89 that is not included in the specified sequence set, it is not
92 This command is particularly useful for disconnected use clients.
93 By using UID EXPUNGE instead of EXPUNGE when resynchronizing with
94 the server, the client can ensure that it does not inadvertantly
95 remove any messages that have been marked as \Deleted by other
96 clients between the time that the client was last connected and
97 the time the client resynchronizes.
99 If the server does not support the UIDPLUS capability, the client
100 should fall back to using the STORE command to temporarily remove
101 the \Deleted flag from messages it does not want to remove, then
102 issuing the EXPUNGE command. Finally, the client should use the
103 STORE command to restore the \Deleted flag on the messages in
104 which it was temporarily removed.
106 Alternatively, the client may fall back to using just the EXPUNGE
107 command, risking the unintended removal of some messages.
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116RFC 4315 IMAP - UIDPLUS Extension December 2005
119 Example: C: A003 UID EXPUNGE 3000:3002
123 S: A003 OK UID EXPUNGE completed
1253. Additional Response Codes
127 The following response codes are extensions to the response codes
128 defined in [IMAP] section 7.1. With limited exceptions, discussed
129 below, server implementations that advertise the UIDPLUS extension
130 SHOULD return these response codes.
132 In the case of a mailbox that has permissions set so that the client
133 can COPY or APPEND to the mailbox, but not SELECT or EXAMINE it, the
134 server SHOULD NOT send an APPENDUID or COPYUID response code as it
135 would disclose information about the mailbox.
137 In the case of a mailbox that has UIDNOTSTICKY status (as defined
138 below), the server MAY omit the APPENDUID or COPYUID response code as
139 it is not meaningful.
141 If the server does not return the APPENDUID or COPYUID response
142 codes, the client can discover this information by selecting the
143 destination mailbox. The location of messages placed in the
144 destination mailbox by COPY or APPEND can be determined by using
145 FETCH and/or SEARCH commands (e.g., for Message-ID or some unique
146 marker placed in the message in an APPEND).
150 Followed by the UIDVALIDITY of the destination mailbox and the UID
151 assigned to the appended message in the destination mailbox,
152 indicates that the message has been appended to the destination
153 mailbox with that UID.
155 If the server also supports the [MULTIAPPEND] extension, and if
156 multiple messages were appended in the APPEND command, then the
157 second value is a UID set containing the UIDs assigned to the
158 appended messages, in the order they were transmitted in the
159 APPEND command. This UID set may not contain extraneous UIDs or
162 Note: the UID set form of the APPENDUID response code MUST NOT
163 be used if only a single message was appended. In particular,
164 a server MUST NOT send a range such as 123:123. This is
165 because a client that does not support [MULTIAPPEND] expects
166 only a single UID and not a UID set.
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172RFC 4315 IMAP - UIDPLUS Extension December 2005
175 UIDs are assigned in strictly ascending order in the mailbox
176 (refer to [IMAP], section 2.3.1.1) and UID ranges are as in
177 [IMAP]; in particular, note that a range of 12:10 is exactly
178 equivalent to 10:12 and refers to the sequence 10,11,12.
180 This response code is returned in a tagged OK response to the
185 Followed by the UIDVALIDITY of the destination mailbox, a UID set
186 containing the UIDs of the message(s) in the source mailbox that
187 were copied to the destination mailbox and containing the UIDs
188 assigned to the copied message(s) in the destination mailbox,
189 indicates that the message(s) have been copied to the destination
190 mailbox with the stated UID(s).
192 The source UID set is in the order the message(s) were copied; the
193 destination UID set corresponds to the source UID set and is in
194 the same order. Neither of the UID sets may contain extraneous
195 UIDs or the symbol "*".
197 UIDs are assigned in strictly ascending order in the mailbox
198 (refer to [IMAP], section 2.3.1.1) and UID ranges are as in
199 [IMAP]; in particular, note that a range of 12:10 is exactly
200 equivalent to 10:12 and refers to the sequence 10,11,12.
202 This response code is returned in a tagged OK response to the COPY
207 The selected mailbox is supported by a mail store that does not
208 support persistent UIDs; that is, UIDVALIDITY will be different
209 each time the mailbox is selected. Consequently, APPEND or COPY
210 to this mailbox will not return an APPENDUID or COPYUID response
213 This response code is returned in an untagged NO response to the
216 Note: servers SHOULD NOT have any UIDNOTSTICKY mail stores.
217 This facility exists to support legacy mail stores in which it
218 is technically infeasible to support persistent UIDs. This
219 should be avoided when designing new mail stores.
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228RFC 4315 IMAP - UIDPLUS Extension December 2005
231 Example: C: A003 APPEND saved-messages (\Seen) {297}
232 C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
233 C: From: Fred Foobar <foobar@example.com>
234 C: Subject: afternoon meeting
235 C: To: mooch@example.com
236 C: Message-Id: <B27397-0100000@example.com>
238 C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
240 C: Hello Joe, do you think we can meet at 3:30 tomorrow?
242 S: A003 OK [APPENDUID 38505 3955] APPEND completed
243 C: A004 COPY 2:4 meeting
244 S: A004 OK [COPYUID 38505 304,319:320 3956:3958] Done
245 C: A005 UID COPY 305:310 meeting
246 S: A005 OK No matching messages, so nothing copied
252 S: * OK [UNSEEN 1] Message 1 is first unseen
253 S: * OK [UIDVALIDITY 3857529045] Validity session-only
254 S: * OK [UIDNEXT 2] Predicted next UID
255 S: * NO [UIDNOTSTICKY] Non-persistent UIDs
256 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
257 S: * OK [PERMANENTFLAGS (\Deleted \Seen)] Limited
258 S: A007 OK [READ-WRITE] SELECT completed
260 In this example, A003 and A004 demonstrate successful appending and
261 copying to a mailbox that returns the UIDs assigned to the messages.
262 A005 is an example in which no messages were copied; this is because
263 in A003, we see that message 2 had UID 304, and message 3 had UID
264 319; therefore, UIDs 305 through 310 do not exist (refer to section
265 2.3.1.1 of [IMAP] for further explanation). A006 is an example of a
266 message being copied that did not return a COPYUID; and, as expected,
267 A007 shows that the mail store containing that mailbox does not
268 support persistent UIDs.
272 Formal syntax is defined using ABNF [ABNF], which extends the ABNF
273 rules defined in [IMAP]. The IMAP4 ABNF should be imported before
274 attempting to validate these rules.
276 append-uid = uniqueid
278 capability =/ "UIDPLUS"
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284RFC 4315 IMAP - UIDPLUS Extension December 2005
287 command-select =/ uid-expunge
289 resp-code-apnd = "APPENDUID" SP nz-number SP append-uid
291 resp-code-copy = "COPYUID" SP nz-number SP uid-set SP uid-set
293 resp-text-code =/ resp-code-apnd / resp-code-copy / "UIDNOTSTICKY"
294 ; incorporated before the expansion rule of
295 ; atom [SP 1*<any TEXT-CHAR except "]">]
296 ; that appears in [IMAP]
300 uid-set = (uniqueid / uid-range) *("," uid-set)
302 uid-range = (uniqueid ":" uniqueid)
303 ; two uniqueid values and all values
304 ; between these two regards of order.
305 ; Example: 2:4 and 4:2 are equivalent.
307 Servers that support [MULTIAPPEND] will have the following extension
310 append-uid =/ uid-set
311 ; only permitted if client uses [MULTIAPPEND]
312 ; to append multiple messages.
3145. Security Considerations
316 The COPYUID and APPENDUID response codes return information about the
317 mailbox, which may be considered sensitive if the mailbox has
318 permissions set that permit the client to COPY or APPEND to the
319 mailbox, but not SELECT or EXAMINE it.
321 Consequently, these response codes SHOULD NOT be issued if the client
322 does not have access to SELECT or EXAMINE the mailbox.
3246. IANA Considerations
326 This document constitutes registration of the UIDPLUS capability in
327 the imap4-capabilities registry, replacing [RFC2359].
3297. Normative References
331 [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
332 Specifications: ABNF", RFC 4234, October 2005.
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340RFC 4315 IMAP - UIDPLUS Extension December 2005
343 [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
344 VERSION 4rev1", RFC 3501, March 2003.
346 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
347 Requirement Levels", BCP 14, RFC 2119, March 1997.
349 [MULTIAPPEND] Crispin, M., "Internet Message Access Protocol (IMAP) -
350 MULTIAPPEND Extension", RFC 3502, March 2003.
3528. Informative References
354 [RFC2359] Myers, J., "IMAP4 UIDPLUS extension", RFC 2359, June
3579. Changes from RFC 2359
359 This document obsoletes [RFC2359]. However, it is based upon that
360 document, and takes substantial text from it (albeit with numerous
361 clarifications in wording).
363 [RFC2359] implied that a server must always return COPYUID/APPENDUID
364 data; thus suggesting that in such cases the server should return
365 arbitrary data if the destination mailbox did not support persistent
366 UIDs. This document adds the UIDNOTSTICKY response code to indicate
367 that a mailbox does not support persistent UIDs, and stipulates that
368 a UIDPLUS server does not return COPYUID/APPENDUID data when the COPY
369 (or APPEND) destination mailbox has UIDNOTSTICKY status.
374 Networks and Distributed Computing
375 University of Washington
377 Seattle, WA 98105-4527
379 Phone: (206) 543-5762
380 EMail: MRC@CAC.Washington.EDU
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396RFC 4315 IMAP - UIDPLUS Extension December 2005
399Full Copyright Statement
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