Sieve Email Filtering: delivery by mailboxid
draft-gondwana-sieve-mailboxid-01

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EXTRA                                                   B. Gondwana, Ed.
Internet-Draft                                                  FastMail
Updates: 5228 (if approved)                              August 11, 2018
Intended status: Standards Track
Expires: February 12, 2019

              Sieve Email Filtering: delivery by mailboxid
                   draft-gondwana-sieve-mailboxid-01

Abstract

   The OBJECTID capability of the IMAP protocol (I-D.ietf-extra-imap-
   objectid) allows clients to identify mailboxes by a unique identifier
   which survives rename.  In contrast, the Sieve mail filtering
   language (RFC 5228) currently has no such capability.  This memo
   defines a Sieve extension that fills this gap: it adds a method for
   specifying the unique identifier of a mailbox as a target for
   fileinto rules, and a method for testing the existence of a mailbox
   by its unique identifier.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on February 12, 2019.

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

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   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 . . . . . . . . . . . . . .   2
   3.  Sieve capability string . . . . . . . . . . . . . . . . . . .   3
   4.  Argument ":mailboxid" to Command "fileinto" . . . . . . . . .   3
     4.1.  Interaction with "mailbox" extension  . . . . . . . . . .   3
     4.2.  Interaction with "specialuse" extension . . . . . . . . .   4
     4.3.  Interaction with "fcc" extension  . . . . . . . . . . . .   5
   5.  Test ":mailboxidexists" . . . . . . . . . . . . . . . . . . .   5
   6.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  draft-gondwana-sieve-mailboxid-01  . . . . . . . . . . .   7
     10.2.  draft-gondwana-sieve-mailboxid-00  . . . . . . . . . . .   7
   11. TODO  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   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, regardless of how 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

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   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 [I-D.ietf-extra-imap-objectid]
   MAILBOXID.  If that is the case, that mailbox is used for delivery
   instead.  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";
        }

4.1.  Interaction with "mailbox" extension

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

   Example:

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        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 [I-D.ietf-extra-sieve-special-use], if
   a fileinto command has both ":mailboxid" and ":special-use"
   specified, then the mailboxid is resolved first.  If the mailboxid
   does not exist, then the special-use is evaluated next following the
   process specified in [I-D.ietf-extra-sieve-special-use] - this
   includes processing of [RFC5490] ":create" tags to add the special-
   use on creation.

   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:

         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.

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4.3.  Interaction with "fcc" extension

   This document extends the definition of the :fcc argument 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]).

   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" 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:

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      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";
          }
      }

   Not to implementers: this test behaves identically to the
   "mailboxexists" test defined in [RFC5490] but operates on mailboxids
   rather than mailbox names.

6.  Formal Syntax

                  test /= ":mailboxidexists" string-list

                  tag /= ":mailboxid" string

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

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

7.  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
   those documents in [RFC5228], [I-D.ietf-extra-imap-objectid].

8.  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 test for checking for mailbox existence by objectid
                and a new optional argument to fileinto to select the
                destination mailbox using objectid.
   RFC number: this RFC
   Contact address: The EXTRA discussion list <extra@ietf.org>

9.  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 for feedback on the EXTRA
   mailing list.

10.  Changes

   (EDITOR: remove this section before publication)

10.1.  draft-gondwana-sieve-mailboxid-01

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

   o  Document interation with special-use.

   o  Document security considerations around :mailboxid and :create.

10.2.  draft-gondwana-sieve-mailboxid-00

   o  Initial version.

11.  TODO

   Is there a more explicit way to update the grammar?  It seems less
   fully specified than IMAP.

12.  References

12.1.  Normative References

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   [I-D.ietf-extra-imap-objectid]
              Gondwana, B., "IMAP Extension for object identifiers",
              draft-ietf-extra-imap-objectid-08 (work in progress),
              August 2018.

   [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>.

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

   [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>.

12.2.  Informative References

   [I-D.ietf-extra-sieve-fcc]
              Murchison, K. and B. Gondwana, "Sieve Extension: File
              Carbon Copy (Fcc)", draft-ietf-extra-sieve-fcc-03 (work in
              progress), August 2018.

   [I-D.ietf-extra-sieve-special-use]
              Bosch, S., "Sieve Email Filtering: Delivering to Special-
              Use Mailboxes", draft-ietf-extra-sieve-special-use-02
              (work in progress), March 2018.

   [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>.

   [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>.

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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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