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EXTRA                                                   B. Gondwana, Ed.
Internet-Draft                                                  Fastmail
Updates: 5228 (if approved)                                 30 July 2020
Intended status: Standards Track
Expires: 31 January 2021


              Sieve Email Filtering: delivery by mailboxid
                  draft-ietf-extra-sieve-mailboxid-00

Abstract

   The OBJECTID capability of the IMAP protocol (RFC8474) allows clients
   to identify mailboxes by a unique identifier which survives rename.

   This document extends the Sieve mail filtering language (RFC5228) to
   allow using that same unique identifier as a target for fileinto
   rules, and for testing the existance of mailboxes.

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 31 January 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.











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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used In This Document . . . . . . . . . . . . . .   3
   3.  Sieve capability string . . . . . . . . . . . . . . . . . . .   3
   4.  Argument ":mailboxid" to Command "fileinto" . . . . . . . . .   3
     4.1.  Interaction with "mailbox" extension  . . . . . . . . . .   4
     4.2.  Interaction with "specialuse" extension . . . . . . . . .   4
     4.3.  Interaction with "fcc" extension  . . . . . . . . . . . .   5
   5.  Test ":mailboxidexists" . . . . . . . . . . . . . . . . . . .   5
   6.  Interaction with variables extension  . . . . . . . . . . . .   6
   7.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  draft-ietf-sieve-mailboxid-00  . . . . . . . . . . . . .   7
     11.2.  draft-gondwana-sieve-mailboxid-02  . . . . . . . . . . .   7
     11.3.  draft-gondwana-sieve-mailboxid-01  . . . . . . . . . . .   8
     11.4.  draft-gondwana-sieve-mailboxid-00  . . . . . . . . . . .   8
   12. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   13. Informative References  . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Sieve rules are sometimes created using graphical interfaces which
   allow users to select the mailbox to be used as a target for a rule.
   If that mailbox is renamed, the client may also update its internal
   representation of the rule and update the sieve script to match,
   however this is a multi-step process and subject to partial failures.
   Also, if the folder is renamed by a different mechanism (e.g. another
   IMAP client) the rules will get out of sync.

   By extending "fileinto" to reference an immutable mailboxid, sieve
   rules can continue to target the same mailbox, even if it gets
   renamed.





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2.  Conventions Used In This Document

   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.  Sieve capability string

   The server advertises the capability "mailboxid", and scripts which
   use the following extensions MUST explicitly request the capability
   "mailboxid".

   Example:

   require "mailboxid";

4.  Argument ":mailboxid" to Command "fileinto"

   Normally, the "fileinto" command delivers the message in the mailbox
   specified using its positional mailbox argument.  However, if the
   optional ":mailboxid" argument is also specified, the "fileinto"
   command first checks whether a mailbox exists in the user's personal
   namespace [RFC2342] with the specified [RFC8474] MAILBOXID.

   If a matching mailbox is found, that mailbox is used for delivery.

   If there is no such mailbox, the "fileinto" action proceeds as it
   would without the ":mailboxid" argument.

   The tagged argument ":mailboxid" to fileinto consumes one additional
   token, a string with the objectid of the mailbox to file into.

   Example:

   require "fileinto";
   require "mailboxid";

   if header :contains ["from"] "coyote" {
       fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3"
                "INBOX.harassment";
   }








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4.1.  Interaction with "mailbox" extension

   For servers which also support the [RFC5490] mailbox extension, the
   ":create" modifier to fileinto does not create the mailbox with the
   specified mailboxid, however it may be specified and interacts as
   normal with all other extensions.

   Example:

   require "fileinto";
   require "mailboxid";
   require "mailbox";

   fileinto :mailboxid "Fnosuch"
            :create
            "INBOX.no-such-folder";
               # creates INBOX.no-such-folder, but it doesn't
               # get the "Fnosuch" mailboxid.

4.2.  Interaction with "specialuse" extension

   For servers which also support [RFC8579] delivery to special-use
   mailboxes, if a fileinto command has both ":mailboxid" and ":special-
   use" specified, then the mailboxid is resolved first.

   If a mailbox with the specified mailboxid does not exist, then the
   process specified in [RFC8579] is followed - which includes
   processing of [RFC5490] ":create" tags to add the special-use to the
   created mailbox.

   Example:

   require "fileinto";
   require "mailboxid";
   require "special-use";
   if header :contains ["from"] "coyote" {
       fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3"
                :specialuse "\\Junk"
                "INBOX.harassment";
   }

   Example:









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   require "fileinto";
   require "mailboxid";
   require "mailbox";
   require "special-use";

   fileinto :mailboxid "F1234567"
            :specialuse "\\Archive"
            :create
            "INBOX.Archive";
               # creates INBOX.Archive with use \Archive but
               # with a different mailboxid.

4.3.  Interaction with "fcc" extension

   This document extends the definition of the ":fcc" argument defined
   in [RFC8580] so that it can optionally be used with the ":mailboxid"
   argument.

   FCC =/ [":mailboxid" <mailboxid: string>]

   If the optional ":mailboxid" argument is specified with ":fcc", it
   instructs the Sieve interpreter to check whether a mailbox exists
   with the specific mailboxid.  If such a mailbox exists, the generated
   message is filed into that mailbox.  Otherwise, the generated message
   is filed into the ":fcc" target mailbox.

   Example:

   require ["enotify", "fcc", "mailboxid"];
   notify :fcc "INBOX.Sent"
          :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3"
          :message "You got mail!"
          "mailto:ken@example.com";

5.  Test ":mailboxidexists"

   The "mailboxidexists" test is true if all mailboxes listed in the
   "mailboxids" argument exist in the mailstore, and each allows the
   user in whose context the Sieve script runs to "deliver" messages
   into it.  When the mailstore is an IMAP server, "delivery" of
   messages is possible if:

   a) the READ-WRITE response code is present for the mailbox (see
   Section 7.1 of [RFC3501]), if IMAP Access Control List (ACL)
   [RFC4314] is not supported by the server, or

   b) the user has 'p' or 'i' rights for the mailbox (see Section 5.2 of
   [RFC4314]).



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   Note that a successful "mailboxidexists" test for a mailbox doesn't
   necessarily mean that a "fileinto :mailboxid" action on this mailbox
   would succeed.  For example, the "fileinto" action might put user
   over quota.  The "mailboxidexists" test only verifies existence of
   the mailbox and whether the user in whose context the Sieve script
   runs has permissions to execute "fileinto" on it.

   Example:

   require "fileinto";
   require "mailboxid";

   if header :contains ["from"] "coyote" {
       if mailboxidexists "F6352ae03-b7f5-463c-896f-d8b48ee3" {
           fileinto :mailboxid "F6352ae03-b7f5-463c-896f-d8b48ee3"
                               "INBOX.harassment";
       } else {
           fileinto "INBOX.harassment";
       }
   }

   Note to implementers: this test behaves identically to the
   "mailboxexists" test defined in [RFC5490] but operates on mailboxids
   rather than mailbox names.

6.  Interaction with variables extension

   There is no special interaction defined, however as an objectid is a
   string in this document, objectid values can contain variable
   expansions if [RFC5229] is enabled.

7.  Formal Syntax

   test /= "mailboxidexists" string-list

   tag /= ":mailboxid" string

   If [I-D.ietf-extra-sieve-fcc] is supported:

   FCC =/ [":mailboxid" <mailboxid: string>]

8.  Security considerations

   Because mailboxid is always generated by the server, implementations
   MUST NOT allow sieve to make an endrun around this protection by
   creating mailboxes with the specified ID by using ":create" and
   ":mailboxid" in a fileinto rule for a non-existant mailbox.




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   Implementers are referred to the security considerations sections of
   [RFC5228] and [RFC8474].

9.  IANA considerations

   IANA are requested to add a capability to the sieve-extensions
   registry:

   To: iana@iana.org
   Subject: Registration of new Sieve extension

   Capability name: mailboxid
   Description: adds a test for checking mailbox existence by objectid,
                and new optional arguments to fileinto and :fcc which
                allow selecting the destination mailbox by objectid.
   RFC number: this RFC
   Contact address: The EXTRA discussion list <extra@ietf.org>

10.  Acknowledgements

   This document borrows heavily from [RFC5490] for the matching
   mailboxexists test, and from [I-D.ietf-extra-sieve-special-use] for
   an example of modifying the fileinto command.

   Thanks to Ned Freed and Ken Murchison and Alexey Melnikov for
   feedback on the EXTRA mailing list.

11.  Changes

   (EDITOR: remove this section before publication)

11.1.  draft-ietf-sieve-mailboxid-00

   *  Adopted into working group per adoption call on list

   *  Updated references to old drafts which have since been published.

   *  Fixed some typoes and simplified some language.

   *  Removed stray leading colon on mailboxexists (thanks Alexey)

   *  Added :fcc to the IANA registration description (thanks Alexey)

   *  Mentioned that variables can be expanded (thanks Alexey)

11.2.  draft-gondwana-sieve-mailboxid-02





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   *  Update document date by a couple of years!  Ooops, it got
      forgotten after a WGLC which got not dissent.

   *  Create xml2rfc v3 output.

11.3.  draft-gondwana-sieve-mailboxid-01

   *  Switch to :mailboxid tagged parameter value with fallback mailbox
      name.

   *  Document interaction with "mailbox".

   *  Document interaction with "special-use".

   *  Document interaction with "fcc".

   *  Document security considerations around :mailboxid and :create.

11.4.  draft-gondwana-sieve-mailboxid-00

   *  Initial version.

12.  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>.

   [RFC5228]  Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email
              Filtering Language", RFC 5228, DOI 10.17487/RFC5228,
              January 2008, <https://www.rfc-editor.org/info/rfc5228>.

   [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>.

   [RFC2342]  Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342,
              DOI 10.17487/RFC2342, May 1998,
              <https://www.rfc-editor.org/info/rfc2342>.

   [RFC8474]  Gondwana, B., Ed., "IMAP Extension for Object
              Identifiers", RFC 8474, DOI 10.17487/RFC8474, September
              2018, <https://www.rfc-editor.org/info/rfc8474>.

   [RFC8580]  Murchison, K. and B. Gondwana, "Sieve Extension: File
              Carbon Copy (FCC)", RFC 8580, DOI 10.17487/RFC8580, May
              2019, <https://www.rfc-editor.org/info/rfc8580>.



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13.  Informative References

   [RFC5490]  Melnikov, A., "The Sieve Mail-Filtering Language --
              Extensions for Checking Mailbox Status and Accessing
              Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March
              2009, <https://www.rfc-editor.org/info/rfc5490>.

   [I-D.ietf-extra-sieve-special-use]
              Bosch, S., "Sieve Email Filtering: Delivering to Special-
              Use Mailboxes", Work in Progress, Internet-Draft, draft-
              ietf-extra-sieve-special-use-05, 24 January 2019,
              <https://tools.ietf.org/html/draft-ietf-extra-sieve-
              special-use-05>.

   [RFC5229]  Homme, K., "Sieve Email Filtering: Variables Extension",
              RFC 5229, DOI 10.17487/RFC5229, January 2008,
              <https://www.rfc-editor.org/info/rfc5229>.

   [RFC8579]  Bosch, S., "Sieve Email Filtering: Delivering to Special-
              Use Mailboxes", RFC 8579, DOI 10.17487/RFC8579, May 2019,
              <https://www.rfc-editor.org/info/rfc8579>.

   [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>.

   [I-D.ietf-extra-sieve-fcc]
              Murchison, K. and B. Gondwana, "Sieve Extension: File
              Carbon Copy (Fcc)", Work in Progress, Internet-Draft,
              draft-ietf-extra-sieve-fcc-09, 13 January 2019,
              <https://tools.ietf.org/html/draft-ietf-extra-sieve-fcc-
              09>.

Author's Address

   Bron Gondwana (editor)
   Fastmail
   Level 2, 114 William St
   Melbourne  VIC 3000
   Australia

   Email: brong@fastmailteam.com
   URI:   https://www.fastmail.com




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