wdiff rfc9586.original rfc9586.txt

Network Working Group

Internet Engineering Task Force (IETF) A. Melnikov
Internet-Draft
Request for Comments: 9586 Isode
Intended status:
Category: Experimental A. P. Achuthan
Expires: 6 October 2024
ISSN: 2070-1721 V. Nagulakonda
A. Singh
Yahoo!
L. Alves
4 April
May 2024

IMAP Extension for only using Using and returning UIDs
draft-ietf-extra-imap-uidonly-08 Returning Unique Identifiers (UIDs) Only

Abstract

The UIDONLY extension to the Internet Message Access Protocol (RFC
3501/RFC (RFCs
3501 and 9051) allows clients to enable a mode in which information
about mailbox changes is returned using only Unique Identifiers
(UIDs). Message numbers are not returned in responses, responses and can't cannot be
used in requests once this extension is enabled. This helps both
clients and servers to reduce resource usage required to maintain a
map between message numbers and UIDs.

This document defines an experimental IMAP extension.

Status of This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

Internet-Drafts are working documents
evaluation.

This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents valid approved by the IESG are candidates for a maximum any level of six months
Internet Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 6 October 2024.
https://www.rfc-editor.org/info/rfc9586.

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Table of Contents

1. Introduction and Overview . . . . . . . . . . . . . . . . . . 2
2. Document Conventions . . . . . . . . . . . . . . . . . . . . 3
3. The UIDONLY extension . . . . . . . . . . . . . . . . . . . . 3 Extension
3.1. Enabling the UIDONLY extension . . . . . . . . . . . . . . . 4 Extension
3.2. Changes to FETCH/STORE/SEARCH/COPY/MOVE . . . . . . . . . 4
3.3. Changes to UID FETCH/UID FETCH / UID STORE . . . . . . . . . . . . . 4
3.4. Changes to EXPUNGE/UID EXPUNGE . . . . . . . . . . . . . 5 / UID EXPUNGE
3.5. Changes to UID SEARCH . . . . . . . . . . . . . . . . . . 5
3.6. Changes to how other mailbox changes are announced . . . 5 How Other Mailbox Changes Are Announced
3.7. Interaction with the CONDSTORE and QRESYNC extensions . . . . 6 Extensions
3.8. Interaction with other extensions . . . . . . . . . . . . 6 Other Extensions
4. Formal syntax . . . . . . . . . . . . . . . . . . . . . . . . 6 Syntax
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Alternative solutions not taken . . . . . . . . . . . . . . . 7 Solutions Not Taken
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 8
9. Informative References
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9

1. Introduction and Overview

This document defines an extension to the Internet Message Access
Protocol [RFC3501] [RFC9051] for eliminating the use of message
numbers. This extension is compatible with both IMAP4rev1 [RFC3501]
and IMAP4rev2 [RFC9051].

The UIDONLY extension of the Internet Message Access Protocol (RFC
3501/RFC 9051) allows
clients to request that servers only use and return UIDs. This helps
both clients and servers to reduce resource usage required for maintenance of message number to UID map.
maintain a map between message numbers and UIDs.

2. Document Conventions

In protocol examples, this document uses a prefix of "C: " "C:" to denote
lines sent by the client to the server, server and "S: " "S:" for lines sent by the
server to the client. Lines prefixed with "// " "//" are comments
explaining the previous protocol line. These prefixes and comments
are not part of the protocol. Lines without any of these prefixes
are continuations of the previous line, and no line break is present
in the protocol unless specifically mentioned.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

Other capitalised capitalized words are names of IMAP commands or responses
[RFC3501][RFC9051]
[RFC3501] [RFC9051] or keywords from this document.

3. The UIDONLY extension Extension

An IMAP server advertises support for the UIDONLY extension by
including the "UIDONLY" capability in the CAPABILITY response/
response code.

Once the UIDONLY extension is enabled (see Section 3.1), the client
MUST NOT use message sequence numbers (including the special marker
"*") in any arguments to IMAP commands, and the server MUST return a
tagged BAD response if the client uses message sequence numbers. The
server MUST include the UIDREQUIRED response code in such BAD
responses (see below). Additionally, once the UIDONLY extension is
enabled, the server MUST NOT return message sequence numbers in any
response.

The UIDREQUIRED response code is defined as follows:

UIDREQUIRED

UIDREQUIRED: Once the UIDONLY extension is enabled enabled, the server
returns the UIDREQUIRED response code when the client issues a
command that includes message numbers instead of UIDs.

C: 07 FETCH 10000:14589 (UID FLAGS)
S: 07 BAD [UIDREQUIRED] Message numbers are not allowed
once UIDONLY is enabled

The UIDONLY extension affects how information about new, expunged expunged, or
changed messages is returned in unsolicited responses. In
partucular,
particular, it affects responses to UID FETCH/UID STORE/EXPUNGE/UID
EXPUNGE, as well as how unsolicited mailbox changes are announced.

The following subsections describe changes introduced by this
extension in more detail.

3.1. Enabling the UIDONLY extension Extension

As the UIDONLY extension affects how information about new, expunged expunged,
or changed messages is returned in unsolicited responses, it has to
be enabled by the client first using the ENABLE command.

S: * OK [CAPABILITY IMAP4rev1 ENABLE CONDSTORE QRESYNC UIDONLY
AUTH=SCRAM-SHA-256]
C: 01 ENABLE UIDONLY
S: * ENABLED UIDONLY
S: 01 OK ENABLE completed

3.2. Changes to FETCH/STORE/SEARCH/COPY/MOVE

When UIDONLY is enabled, the FETCH, STORE, SEARCH, COPY COPY, and MOVE
commands are prohibited and MUST result in a tagged BAD response.
Clients should instead use UID FETCH, UID STORE, UID SEARCH, UID COPY
COPY, or UID
MOVE MOVE, respectively.

3.3. Changes to UID FETCH/UID FETCH / UID STORE

When UIDONLY is enabled, all FETCH responses that would be returned
by UID FETCH/UID FETCH / UID STORE are replaced by UIDFETCH responses.

Note that the UIDFETCH response contains the same response data items
as specified for the FETCH response. The UID is always returned at
the beginning of a UIDFETCH response, and it can also appear in the
UID response data item, if requested by the client. While the UID
response data item is redundant when requested, it can simplify the
updating of existing (non UIDONLY) (non-UIDONLY) implementations to support
UIDONLY.

C: 10 UID FETCH 25900:26600 (FLAGS)
[...]
S: * 25996 UIDFETCH (FLAGS (\Seen))
S: * 25997 UIDFETCH (FLAGS (\Flagged \Answered))
S: * 26600 UIDFETCH (FLAGS ())
S: 10 OK FETCH completed

C: 11 UID FETCH 25900:26600 (UID FLAGS)
S: * 25900 UIDFETCH (FLAGS (\Seen) UID 25900)
S: * 25902 UIDFETCH (FLAGS (\Flagged) UID 25902)
S: * 26310 UIDFETCH (FLAGS (\Answered) UID 26310)
S: * 26311 UIDFETCH (FLAGS () UID 26311)
S: * 26498 UIDFETCH (FLAGS (\Answered) UID 26498)
[...]
S: 11 OK FETCH completed

3.4. Changes to EXPUNGE/UID EXPUNGE / UID EXPUNGE

When UIDONLY is enabled, all EXPUNGED responses that would be
returned by EXPUNGE/UID EXPUNGE / UID EXPUNGE are replaced by VANISHED responses,
as defined in [RFC7162]. Note that a server that implements the
UIDONLY extension is not required (but allowed) to also implement the
CONDSTORE and/or QRESYNC extensions.

C: 12 EXPUNGE
S: * VANISHED 405,407,410,425
S: 12 OK expunged

3.5. Changes to UID SEARCH

The "<sequence set>" UID SEARCH criterion is prohibited (and results
in a tagged BAD response) once UIDONLY is enabled. Clients should
use ALL or "UID <sequence set>" UID SEARCH criterion instead.

3.6. Changes to how other mailbox changes are announced How Other Mailbox Changes Are Announced

When UIDONLY is enabled, all changes to flags (and other dynamic
message attributes) are returned using UIDFETCH responses, responses instead of
FETCH responses.

Similarly, all expunged messages are announced using VANISHED
responses instead of EXPUNGE responses.

This extension doesn't affect EXISTS or RECENT responses.

The UID MOVE / UID MOVE/UID COPY commands SHOULD return the COPYUID response
code, as specified in [RFC4315].

Use of the UIDNOTSTICKY response code (see [RFC4315]) is not
compatible with the UIDONLY extension, i.e. i.e., a server that advertises
the UIDONLY extension MUST NOT return a UIDNOTSTICKY response code.

C: 15 UID move 597 "Archives/2023/2023-05"
S: * OK [COPYUID 1685977201 597 2] UID MOVE
S: * VANISHED 597
S: 15 OK UID MOVE Completed

3.7. Interaction with the CONDSTORE and QRESYNC extensions Extensions

The CONDSTORE extension is compatible with the UIDONLY extension.
The MODSEQ message data item is returned in UIDFETCH responses
instead of FETCH responses.

The QRESYNC extension is compatible with the UIDONLY extension, but
once UIDONLY is enabled, the fourth SELECT QRESYNC parameter (see
Section 3.2.5.2 ("Message Sequence Match Data", see Section 3.2.5.2 Data") of [RFC7162]) MUST
NOT be used. The server MUST return a tagged BAD response if such a
parameter is observed once UIDONLY is enabled.

3.8. Interaction with other extensions Other Extensions

IMAP extensions might define other commands that accept message
sequence numbers ("sequence-set" ABNF non terminal, non-terminal; see Section 9 of
[RFC9051]). Once UIDONLY is enabled, the server MUST reject such
commands with a tagged BAD response. For example, the SORT and
THREAD [RFC5256] commands are prohibited, similarly to the SEARCH
command.
However However, UID SORT and UID THREAD can be used instead.

4. Formal syntax Syntax

The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].

Non-terminals referenced but not defined below are as defined by in
Section 9 of IMAP4 [RFC9051].

Except as noted otherwise, all alphabetic characters are case- case
insensitive. The use of upper uppercase or lower case lowercase characters to define
token strings is for editorial clarity only. Implementations MUST
accept these strings in a case-insensitive fashion.

SP = <Defined in RFC 5234>

capability =/ "UIDONLY"
;; <capability> from [RFC9051] <capability>; see RFC 9051

message-data =/ uidfetch-resp

uidfetch-resp = uniqueid SP "UIDFETCH" SP msg-att
;; The uniqueid is the UID of
;; the corresponding message

message-data =/ expunged-resp

expunged-resp = <defines VANISHED response, response; see RFC 7162>

resp-text-code =/ "UIDREQUIRED"

5. Security Considerations

This IMAP extension is not believed to add any additional Security
Considerations beyond the ones that are generally applicable to
IMAP4rev1 [RFC3501] and IMAP4rev2 [RFC9051].

6. IANA Considerations

IMAP4 capabilities are registered by publishing a standards track Standards Track or
IESG approved
IESG-approved Informational or Experimental RFC. The registry is
currently located at:

https://www.iana.org/assignments/imap4-capabilities

IANA is requested to add definition of has added the UIDONLY extension to this the "IMAP Capabilities"
registry with [RFCXXXX] RFC 9586 as the reference.

IANA The registry is located at
<https://www.iana.org/assignments/imap4-capabilities/>.

IANA has also requested to add definition of added the UIDREQUIRED response code to the "IMAP
Response Codes" registry with [RFCXXXX] RFC 9586 as the reference. The
registry is currently located at:

https://www.iana.org/assignments/imap-response-codes/imap-response-codes.xhtml at <https://www.iana.org/assignments/imap-
response-codes/>.

7. Alternative solutions not taken Solutions Not Taken

An earlier draft version of this document proposed use of FETCH
responses with the message number parameter always be set to 0. This
was
judged considered to be too risky, risky as this it could have caused cause unexpected side
effects and cache corruptions in client code that was not properly
updated to handle a lack of message numbers.

8. Acknowledgments

Editors of this document would like to thank the following people who
provided useful comments and/or participated in discussions that lead
to this document, in particular: Arnt Gulbrandsen, Ken Murchison,
Bron Gondwana, Barry Leiba and Elwyn Davis.

This document is similar to draft-gulbrandsen-imap-uidonly-00.txt,
but some different syntactic choices were made in the end.

9. Normative References

[ABNF] Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>.

[RFC4315] Crispin, M., "Internet Message Access Protocol (IMAP) -
UIDPLUS extension", RFC 4315, DOI 10.17487/RFC4315,
December 2005, <https://www.rfc-editor.org/info/rfc4315>.

[RFC5256] Crispin, M. and K. Murchison, "Internet Message Access
Protocol - SORT and THREAD Extensions", RFC 5256,
DOI 10.17487/RFC5256, June 2008,
<https://www.rfc-editor.org/info/rfc5256>.

[RFC7162] Melnikov, A. and D. Cridland, "IMAP Extensions: Quick Flag
Changes Resynchronization (CONDSTORE) and Quick Mailbox
Resynchronization (QRESYNC)", RFC 7162,
DOI 10.17487/RFC7162, May 2014,
<https://www.rfc-editor.org/info/rfc7162>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC9051] Melnikov, A., Ed. and B. Leiba, Ed., "Internet Message
Access Protocol (IMAP) - Version 4rev2", RFC 9051,
DOI 10.17487/RFC9051, August 2021,
<https://www.rfc-editor.org/info/rfc9051>.

9. Informative References

[IMAP-UIDONLY-ORIG]
Gulbrandsen, A., "The IMAP UIDONLY Extension", Work in
Progress, Internet-Draft, draft-gulbrandsen-imap-uidonly-
00, 25 April 2014, <https://datatracker.ietf.org/doc/html/
draft-gulbrandsen-imap-uidonly-00>.

Acknowledgments

The editors of this document would like to thank the following people
who provided useful comments and/or participated in discussions that
lead to this document: Arnt Gulbrandsen, Ken Murchison, Bron
Gondwana, Barry Leiba, and Elwyn Davis.

This document is similar to [IMAP-UIDONLY-ORIG], but some different
syntactic choices were made in the end.

Authors' Addresses

Alexey Melnikov
Isode Limited
Email: alexey.melnikov@isode.com
URI: https://www.isode.com

Arun Prakash Achuthan
Yahoo Inc.
Email: arunprakash@myyahoo.com

Vikram Nagulakonda
Yahoo Inc.
Email: nvikram_imap@yahoo.com

Ashutosh Singh
Yahoo Inc.
Email: ashutoshvsingh@yahoo.com

Luis Alves
Email: luis.alves@lafaspot.com