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IMAP4 Extension for Returning Mailbox METADATA in Extended LIST
draft-ietf-extra-imap-list-metadata-01

Document Type Active Internet-Draft (extra WG)
Authors Kenneth Murchison , Bron Gondwana
Last updated 2024-02-22 (Latest revision 2023-12-18)
Replaces draft-murchison-imap-list-metadata
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Formats
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Associated WG milestone
Dec 2023
Submit LIST-METADATA draft to IESG
Document shepherd Arnt Gulbrandsen
Shepherd write-up Show Last changed 2024-02-21
IESG IESG state Publication Requested
Action Holder
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Murray Kucherawy
Send notices to arnt.gulbrandsen@icann.org
draft-ietf-extra-imap-list-metadata-01
EXTRA                                                       K. Murchison
Internet-Draft                                               B. Gondwana
Intended status: Standards Track                                Fastmail
Expires: 20 June 2024                                   18 December 2023

    IMAP4 Extension for Returning Mailbox METADATA in Extended LIST
                 draft-ietf-extra-imap-list-metadata-01

Abstract

   This document defines an extension to the to IMAP LIST command that
   allows the client to request mailbox annotations (metadata), along
   with other information typically returned by the LIST command.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents 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 20 June 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  METADATA Return Option to LIST Command  . . . . . . . . . . .   3
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Registration of IMAP capability LIST-METADATA . . . . . .   4
     8.2.  Registration of LIST-EXTENDED option METADATA . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Change History (To be removed by RFC Editor before
           publication)  . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IMAP clients sometimes fetch mailbox metadata (e.g. color) to augment
   the display of mailboxes to the logged-in user.  In order to do that,
   the client is forced to issue a LIST or LSUB command to list all
   available mailboxes, followed by a GETMETADATA command for each
   mailbox found.  This document defines an extension to the to IMAP
   LIST command that is identified by the capability string "LIST-
   METADATA".  The LIST-METADATA extension allows the client to request
   annotations on available mailboxes, along with other information
   typically returned by the LIST command.

2.  Conventions Used in This Document

   In examples, "C:" indicates lines sent by a client that is connected
   to a server.  "S:" indicates lines sent by the server to the client.

   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.

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3.  METADATA Return Option to LIST Command

   [RFC5464] defines the GETMETADATA command which is used by an IMAP
   client to retrieve mailbox annotations.  Sometimes, a client will
   have to look up the metadata for some or all of the mailboxes
   returned by the LIST command.  Doing so in multiple GETMETADATA
   commands wastes bandwidth and can degrade performance if the client
   does not pipeline the requests.

   This document extends the LIST command with a new return option,
   "METADATA", which allows the client to request all of the desired
   information in a single command.  For each listable mailbox matching
   the list pattern and selection options, the server MUST return an
   untagged LIST response followed by one or more untagged METADATA
   responses containing the mailbox annotations requested by the client.
   The untagged METADATA responses to an extended LIST command have the
   same syntax and semantics as those that would be returned by
   GETMETADATA commands on the same set of listable mailboxes (see
   Section 4.4.1 of [RFC5464]).  As per Section 4.4 of [RFC5464], the
   server may return all requested annotations in a single METADATA
   response for each mailbox, or it may split the requested annotations
   into multiple METADATA responses for each mailbox.

   If the server is unable to look up the annotations for given mailbox,
   it MAY drop the corresponding METADATA response.  In such a
   situation, the LIST command would still return a tagged OK reply.

4.  Examples

   Note that the line wrapping of the extended LIST commands below is
   for editorial purposes only.

   In this example:

   *  The "color" annotation for the "foo" mailbox has not been set, so
      the METADATA response has a value of "NIL" (has no value).

   *  The "bar" mailbox doesn't exist, so it has no METADATA response.

  C: A01 LIST "" %
           RETURN (METADATA ("/shared/vendor/cmu/cyrus-imapd/color"))
  S: * LIST () "." "INBOX"
  S: * METADATA INBOX ("/shared/vendor/cmu/cyrus-imapd/color" "#b71c1c")
  S: * LIST () "." "foo"
  S: * METADATA "foo" ("/shared/vendor/cmu/cyrus-imapd/color" NIL)
  S: * LIST (\NonExistent) "." "bar"
  S: A01 OK List completed.

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   In this example the LIST response for the "foo" mailbox is returned
   because it has matching children, but no METADATA response is
   returned because "foo" itself doesn't match the selection criteria.

  C: A02 LIST (SUBSCRIBED RECURSIVEMATCH) "" %
           RETURN (METADATA ("/shared/vendor/cmu/cyrus-imapd/color"))
  S: * LIST (\Subscribed) "." "INBOX"
  S: * METADATA INBOX ("/shared/vendor/cmu/cyrus-imapd/color" "#b71c1c")
  S: * LIST () "." "foo" (CHILDINFO ("SUBSCRIBED"))
  S: A02 OK List completed.

5.  Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in [RFC5234].  Note that "return-option" is
   defined in [RFC5258] and "entry" is defined in [RFC5464].

   return-option =/ "METADATA" SP "(" entry *(SP entry) ")"

6.  Security Considerations

   This specification does not introduce any additional security
   concerns beyond those described in [RFC5258].

7.  Privacy Considerations

   This specification does not introduce any additional privacy concerns
   beyond those described in [RFC5464].

8.  IANA Considerations

8.1.  Registration of IMAP capability LIST-METADATA

   This document defines the "LIST-METADATA" IMAP capability to be added
   to the registry defined in Section 12.1 of [RFC9051].

8.2.  Registration of LIST-EXTENDED option METADATA

   This section registers the "METADATA" option to be added to the
   registry defined in Section 9 of [RFC5258].

   LIST-EXTENDED option name:
      METADATA

   LIST-EXTENDED option type:
      RETURN

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   LIST-EXTENDED option description:
      Causes the LIST command to return METADATA responses in addition
      to LIST responses.

   Published specification:
      RFC XXXX, Section 3

   Security considerations:
      RFC XXXX, Section 6

   Intended usage:
      COMMON

   Person and email address to contact for further information:
      Kenneth Murchison <murch@fastmailteam.com>, Bron Gondwana
      <brong@fastmailteam.com>

   Owner/Change controller:
      IESG <iesg@ietf.org>

9.  References

9.1.  Normative References

   [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>.

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

   [RFC5258]  Leiba, B. and A. Melnikov, "Internet Message Access
              Protocol version 4 - LIST Command Extensions", RFC 5258,
              DOI 10.17487/RFC5258, June 2008,
              <https://www.rfc-editor.org/info/rfc5258>.

   [RFC5464]  Daboo, C., "The IMAP METADATA Extension", RFC 5464,
              DOI 10.17487/RFC5464, February 2009,
              <https://www.rfc-editor.org/info/rfc5464>.

   [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>.

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   [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>.

Appendix A.  Change History (To be removed by RFC Editor before
             publication)

   Changes from draft-ietfextra-imap-list-metadata-00:

   *  Added missing SP in ABNF.

   Changes from draft-murchison-imap-list-metadata-02:

   *  Renamed as a WG document.

   *  Clarified that the METADATA response with values is used.

   *  Miscellaneous editorial changes.

   Changes from draft-murchison-imap-list-metadata-01:

   *  None.

   Changes from draft-murchison-imap-list-metadata-00:

   *  Updated Keywords boilerplate.

   *  Changed RFC 3501 reference to RFC 9051.

Authors' Addresses

   Kenneth Murchison
   Fastmail US LLC
   1429 Walnut Street - Suite 1201
   Philadelphia, PA 19102
   United States of America
   Email: murch@fastmailteam.com

   Bron Gondwana
   Fastmail Pty Ltd
   Level 2, 114 William Street
   Melbourne VIC 3000
   Australia
   Email: brong@fastmailteam.com

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