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RFC 8440

IMAP4 Extension for Returning MYRIGHTS Information in Extended LIST

Pages: 6
Proposed Standard

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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