IMAP4 Extension for Returning Mailbox METADATA in Extended LIST
draft-murchison-imap-list-metadata-00

EXTRA                                                       K. Murchison
Internet-Draft                                               B. Gondwana
Intended status: Standards Track                                Fastmail
Expires: 23 March 2023                                 19 September 2022

    IMAP4 Extension for Returning Mailbox METADATA in Extended LIST
                 draft-murchison-imap-list-metadata-00

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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  METADATA Return Option to LIST Command  . . . . . . . . . . .   2
   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
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

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
   [RFC2119].

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.

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   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.  As per
   [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 it desires.

   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.

   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.

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  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" "(" 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 of [RFC3501].

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

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

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   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>.

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

   [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>.

Authors' Addresses

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   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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