Sieve Email Filtering: delivery by mailboxid
draft-ietf-extra-sieve-mailboxid-09

Document Type Active Internet-Draft (extra WG)
Author Bron Gondwana 
Last updated 2021-04-05 (latest revision 2021-03-16)
Replaces draft-gondwana-sieve-mailboxid
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EXTRA                                                   B. Gondwana, Ed.
Internet-Draft                                                  Fastmail
Updates: 5228 (if approved)                                16 March 2021
Intended status: Standards Track                                        
Expires: 17 September 2021

              Sieve Email Filtering: delivery by mailboxid
                  draft-ietf-extra-sieve-mailboxid-09

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 17 September 2021.

Copyright Notice

   Copyright (c) 2021 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
   5.  Interaction with "fcc" extension  . . . . . . . . . . . . . .   5
   6.  Test "mailboxidexists"  . . . . . . . . . . . . . . . . . . .   5
   7.  Interaction with variables extension  . . . . . . . . . . . .   6
   8.  Security considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   6
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  draft-ietf-sieve-mailboxid-09  . . . . . . . . . . . . .   7
     11.2.  draft-ietf-sieve-mailboxid-08  . . . . . . . . . . . . .   7
     11.3.  draft-ietf-sieve-mailboxid-07  . . . . . . . . . . . . .   7
     11.4.  draft-ietf-sieve-mailboxid-06  . . . . . . . . . . . . .   8
     11.5.  draft-ietf-sieve-mailboxid-05  . . . . . . . . . . . . .   8
     11.6.  draft-ietf-sieve-mailboxid-04  . . . . . . . . . . . . .   8
     11.7.  draft-ietf-sieve-mailboxid-03  . . . . . . . . . . . . .   8
     11.8.  draft-ietf-sieve-mailboxid-02  . . . . . . . . . . . . .   8
     11.9.  draft-ietf-sieve-mailboxid-01  . . . . . . . . . . . . .   8
     11.10. draft-ietf-sieve-mailboxid-00  . . . . . . . . . . . . .   8
     11.11. draft-gondwana-sieve-mailboxid-02  . . . . . . . . . . .   9
     11.12. draft-gondwana-sieve-mailboxid-01  . . . . . . . . . . .   9
     11.13. draft-gondwana-sieve-mailboxid-00  . . . . . . . . . . .   9
   12. Normative References  . . . . . . . . . . . . . . . . . . . .   9
   13. Informative References  . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC5228] Sieve rules are sometimes created using graphical
   interfaces which allow users to select the mailbox to be used as a
   target for a rule.

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   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 telling "fileinto" to reference the immutable mailboxid specified
   by [RFC8474], using the extension specified herein, sieve rules can
   continue to target the same mailbox even if it gets renamed.

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

   Scripts which use the following extensions MUST explicitly require
   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:

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   require "fileinto";
   require "mailboxid";

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

4.1.  Interaction with "mailbox" extension

   For servers which also support the [RFC5490] mailbox extension, if
   both the ":create" and ":mailboxid" arguments are provided to a
   "fileinto" command and no matching mailbox is found, then a new
   mailbox will be created.

   This new mailbox will have the name specified by the positional
   mailbox argument ([RFC5228] section 4.1), however it will get a
   different mailboxid (chosen by the server) rather than the one
   specified by the ":mailboxid" argument to fileinto.

   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, it is an error to specify both ":mailboxid" and
   ":specialuse" in the same fileinto command.

   Advanced filtering based on both special-use and mailboxid can be
   built with explicit "specialuse_exists" and "mailboxidexists" tests.

   Note to developers of sieve generation tools: it is advisable to use
   special-use rather than mailboxid when creating rules that are based
   on a special-use purpose (e.g. delivery directly to the Junk folder
   based on a header that was added by a scanning agent earlier in the
   mailflow).

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5.  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.  The syntax for "FCC" is extended here using ABNF
   [RFC5234]:

   MAILBOXID-OPT = ":mailboxid" objectid

   FCC-OPTS =/ MAILBOXID-OPT

   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.

   As with fileinto, it is an error to specify both ":mailboxid" and
   ":specialuse" for the same fcc rule.

   Example:

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

6.  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.name.will.not.be.used";
       } 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.

7.  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.

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.

   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:

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   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 [RFC8579] 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-09

   *  update FCC-OPTS to have an intermediate production for the
      :mailboxid option, and reference "objectid" from RFC8474 as the
      valid format for the option value.

11.2.  draft-ietf-sieve-mailboxid-08

   *  IETF110 discussion - re-add FCC-OPTS syntax, and clarify that
      :mailboxid is incompatible with :specialuse to parallel the
      fileinto behaviour

11.3.  draft-ietf-sieve-mailboxid-07

   *  Martin Duke review - remove formal section

   *  Martin Duke review - wording for section 4.1 (interaction with
      :create)

   *  Ken Murchison review - fixed :special-use to :specialuse per
      RFC8579

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11.4.  draft-ietf-sieve-mailboxid-06

   *  GENART review - fixed example to not be semantically pointless

   *  GENART review - fixed !@ to @! in RFC reference mmark syntax

11.5.  draft-ietf-sieve-mailboxid-05

   *  disallow :mailboxid and :special-use in the same fileinto action.

11.6.  draft-ietf-sieve-mailboxid-04

   *  made RFC5490 and RFC8579 normative

   *  clarified wording based on AD feedback from Barry

11.7.  draft-ietf-sieve-mailboxid-03

   *  Fixed ABNF syntax error

11.8.  draft-ietf-sieve-mailboxid-02

   *  removed bogus : from "mailboxidexists" test title

   *  moved FCC to its own top-level section since it is not used with
      the fileinto command.

11.9.  draft-ietf-sieve-mailboxid-01

   *  fixed idnits - RFC5228 not mentioned in the abstract

   *  fixed other I-D references I had missed, oops

11.10.  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)

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11.11.  draft-gondwana-sieve-mailboxid-02

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

   *  Create xml2rfc v3 output.

11.12.  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.

11.13.  draft-gondwana-sieve-mailboxid-00

   *  Initial version.

12.  Normative References

   [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>.

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

   [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>.

   [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>.

   [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>.

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

   [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>.

13.  Informative References

   [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>.

   [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>.

   [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>.

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

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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