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RFC 8440

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IMAP4 Extension for Returning MYRIGHTS Information in Extended LIST

 


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Internet Engineering Task Force (IETF)                      K. Murchison
Request for Comments: 8440                                   B. Gondwana
Category: Standards Track                                       FastMail
ISSN: 2070-1721                                              August 2018


  IMAP4 Extension for Returning MYRIGHTS Information in Extended LIST

Abstract

   This document defines an extension to the Internet Message Access
   Protocol (IMAP) LIST command that allows the client to request the
   set of rights that the logged-in user has been granted on mailboxes,
   along with other information typically returned by the LIST command.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8440.

Copyright Notice

   Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  MYRIGHTS 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-MYRIGHTS . . . . . .   4
     8.2.  Registration of LIST-EXTENDED Option MYRIGHTS . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IMAP [RFC3501] clients typically fetch the set of rights granted on
   mailboxes so they can expose the allowed functionality 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
   MYRIGHTS command for each mailbox found.  This document defines an
   extension to the to IMAP LIST command that is identified by the
   capability string "LIST-MYRIGHTS".  The LIST-MYRIGHTS extension
   allows the client to request the set of rights that the logged-in
   user has been granted on 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.

3.  MYRIGHTS Return Option to LIST Command

   [RFC4314] defines the MYRIGHTS command, which is used by an IMAP
   client to determine the set of rights that the logged-in user has
   been granted on a given mailbox.  Frequently, a client will have to
   look up the rights for some or all of the mailboxes returned by the

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   LIST command.  Doing so in multiple MYRIGHTS commands wastes
   bandwidth and can degrade performance if the client does not pipeline
   the requests.

   This document extends the LIST command with a new "MYRIGHTS" return
   option [RFC5258] that 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 and SHOULD also return an untagged MYRIGHTS
   response containing the set of rights granted to the logged-in user.
   The ordering of the responses is significant only in that the server
   MUST NOT send a MYRIGHTS response for a given mailbox before it sends
   the LIST response for that mailbox.

   If the server is unable to look up the set of rights for a given
   mailbox, it does not send the MYRIGHTS reply for that mailbox.

   Client authors ought to note that generating the MYRIGHTS responses
   for a large number of mailboxes may be an expensive operation for the
   server.  Clients SHOULD use a suitable match pattern and/or selection
   option to limit the set of mailboxes returned to only those in whose
   rights they are interested.

4.  Examples

   In this example, the "bar" mailbox doesn't exist, so it has no
   MYRIGHTS reply.

   C: A01 LIST "" % RETURN (MYRIGHTS)
   S: * LIST () "." "INBOX"
   S: * MYRIGHTS "INBOX" lrswipkxtecda
   S: * LIST () "." "foo"
   S: * MYRIGHTS "foo" lrs
   S: * LIST (\NonExistent) "." "bar"
   S: A01 OK List completed.

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

   C: A02 LIST (SUBSCRIBED RECURSIVEMATCH) "" % RETURN (MYRIGHTS)
   S: * LIST (\Subscribed) "." "INBOX"
   S: * MYRIGHTS "INBOX" lrswipkxtecda
   S: * LIST () "." "foo" (CHILDINFO ("SUBSCRIBED"))
   S: A02 OK List completed.

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5.  Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in [RFC5234].  Terms not defined here are
   taken from [RFC5258].

   return-option =/ "MYRIGHTS"

6.  Security Considerations

   In addition to the security considerations described in [RFC4314],
   this extension makes it a bit easier for clients to overload the
   server by requesting MYRIGHTS information for a large number of
   mailboxes.  However, as noted in the introduction, existing clients
   already try to do that by generating a large number of MYRIGHTS
   commands for each mailbox in which they are interested.  While
   performing MYRIGHTS information retrieval for big lists of mailboxes,
   a server implementation needs to make sure that it can still serve
   other IMAP connections and yield execution to other connections, when
   necessary.

7.  Privacy Considerations

   This specification does not introduce any additional privacy concerns
   beyond those described in [RFC4314].

8.  IANA Considerations

8.1.  Registration of IMAP Capability LIST-MYRIGHTS

   This document defines the "LIST-MYRIGHTS" IMAP capability that has
   been added to the "IMAP Capabilities" registry [CAPABILITIES].

8.2.  Registration of LIST-EXTENDED Option MYRIGHTS

   This section registers the "MYRIGHTS" option that has been added to
   the "LIST-EXTENDED options" registry [EXTENDED].

   LIST-EXTENDED option name:  MYRIGHTS

   LIST-EXTENDED option type:  RETURN

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

   Published specification:  RFC 8440, Section 3

   Security considerations:  RFC 8440, Section 6

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   Intended usage:  COMMON

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

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

9.  References

9.1.  Normative References

   [CAPABILITIES]
              IANA, "Internet Message Access Protocol (IMAP)
              Capabilities Registry", <https://www.iana.org/assignments/
              imap-capabilities/imap-capabilities>.

   [EXTENDED]
              IANA, "Internet Message Access Protocol (IMAP) LIST
              EXTENDED Registry",
              <https://www.iana.org/assignments/imap-list-extended>.

   [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>.

   [RFC4314]  Melnikov, A., "IMAP4 Access Control List (ACL) Extension",
              RFC 4314, DOI 10.17487/RFC4314, December 2005,
              <https://www.rfc-editor.org/info/rfc4314>.

   [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>.

   [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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9.2.  Informative References

   [RFC5819]  Melnikov, A. and T. Sirainen, "IMAP4 Extension for
              Returning STATUS Information in Extended LIST", RFC 5819,
              DOI 10.17487/RFC5819, March 2010,
              <https://www.rfc-editor.org/info/rfc5819>.

Acknowledgments

   This document is based largely on [RFC5819].  The authors would like
   to thank the authors of that document for providing both inspiration
   and some borrowed text for this document.  The authors would also
   like to thank Barry Leiba for contributing his ideas and support for
   writing this specification.

Authors' Addresses

   Kenneth Murchison
   FastMail Pty Ltd.
   Level 2, 114 William Street
   Melbourne, VIC  3000
   Australia

   Email: murch@fastmailteam.com


   Bron Gondwana
   FastMail Pty Ltd.
   Level 2, 114 William Street
   Melbourne, VIC  3000
   Australia

   Email: brong@fastmailteam.com