IMAP Extension for only using and returning UIDs
draft-ietf-extra-imap-uidonly-00

Network Working Group                                        A. Melnikov
Internet-Draft                                                     Isode
Intended status: Standards Track                          A. P. Achuthan
Expires: 3 August 2023                                    V. Nagulakonda
                                                                A. Singh
                                                                  Yahoo!
                                                                L. Alves
                                                         30 January 2023

            IMAP Extension for only using and returning UIDs
                    draft-ietf-extra-imap-uidonly-00

Abstract

   The UIDONLY extension of the Internet Message Access Protocol (RFC
   3501/RFC 9051) allows clients to request that all information about
   mailbox changes is returned only using UIDs.  Message numbers are not
   going to be returned and can't be used once this extension is
   enabled.  This helps both clients and servers to reduce resource
   usage required for maintenance of message number to UID map.

Status of This Memo

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   This Internet-Draft will expire on 3 August 2023.

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
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Table of Contents

   1.  Introduction and Overview . . . . . . . . . . . . . . . . . .   2
   2.  Document Conventions  . . . . . . . . . . . . . . . . . . . .   3
   3.  The UIDONLY extension . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Enabling UIDONLY extension  . . . . . . . . . . . . . . .   3
     3.2.  Changes to FETCH/STORE/SEARCH . . . . . . . . . . . . . .   4
     3.3.  Changes to UID FETCH/UID STORE  . . . . . . . . . . . . .   4
     3.4.  Changes to EXPUNGE/UID EXPUNGE  . . . . . . . . . . . . .   4
     3.5.  Changes to how other mailbox changes are announced  . . .   5
   4.  Formal syntax . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Changes/additions to the IMAP4 capabilities registry  . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction and Overview

   This document defines an extension to the Internet Message Access
   Protocol [RFC3501] for eliminating 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.

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   IMPLEMENTATION NOTE: this document is not yet at the state where it
   is implementable.  Please contact document authors if you want to
   experiment with implementing UIDONLY.

2.  Document Conventions

   In protocol examples, this document uses a prefix of "C: " to denote
   lines sent by the client to the server, and "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 words are IMAP keywords [RFC3501][RFC9051] or
   keywords from this document.

3.  The UIDONLY extension

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

   The UIDONLY extension affects how information about new, expunged or
   changed messages is returned in unsolicited responses.  In
   partucular, 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 details.

3.1.  Enabling UIDONLY extension

   As the UIDONLY extension affects how information about new, 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

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3.2.  Changes to FETCH/STORE/SEARCH

   // Is this Ok or is this too restrictive?  Should COPY/MOVE be
   // restricted in the same way?

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

3.3.  Changes to UID FETCH/UID STORE

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

   Note that UIDFETCH response contains the same FETCH response data
   items, except the UID, which is returned differently at the beginning
   of a UIDFETCH response.  Requesting UID FETCH data item is not an
   error and this is just ignored.

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

3.4.  Changes to EXPUNGE/UID EXPUNGE

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

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

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3.5.  Changes to how other mailbox changes are announced

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

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

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

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

   // Also need to think about interaction with CONDSTORE/QRESYNC in
   // more details.  CONDSTORE is compatible with UIDONLY, but QRESYNC
   // might not be, due to existence of message numbers in SELECT
   // QRESYNC.

4.  Formal 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
   IMAP4 [RFC3501].

   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.

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SP                  = <Defined in RFC 5234>

capability          =/ "UIDONLY"
                       ;; <capability> from [RFC3501]

message-data        =/ uidfetch-resp

uidfetch-resp       = uniqueid SP "UIDFETCH" SP msg-att
                      ;; UID msg-att is never used. It is replaced by the uniqueid
                      ;; at the beginning of the UIDFETCH response

message-data        =/ expunged-resp

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

5.  Security Considerations

   TBD.

6.  IANA Considerations

6.1.  Changes/additions to the IMAP4 capabilities registry

   IMAP4 capabilities are registered by publishing a standards track or
   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 the UIDONLY extension to point
   to this document.

7.  Acknowledgments

   TBD.

8.  Normative References

   [ABNF]     Crocker, D., Ed. and P. Overell, Ed., "Augmented BNF for
              Syntax Specifications: ABNF", RFC 5234, 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>.

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   [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>.

   [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>.

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

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