Sieve Email Filtering: delivery by mailboxid
draft-gondwana-sieve-mailboxid-00

EXTRA                                                   B. Gondwana, Ed.
Internet-Draft                                                  FastMail
Updates: 7162 (if approved)                              August 11, 2018
Intended status: Standards Track
Expires: February 12, 2019

              Sieve Email Filtering: delivery by mailboxid
                   draft-gondwana-sieve-mailboxid-00

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

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used In This Document . . . . . . . . . . . . . .   2
   3.  Capability argument . . . . . . . . . . . . . . . . . . . . .   3
   4.  Argument ":mailboxid" to Command "fileinto" . . . . . . . . .   3
   5.  Test ":mailboxidexists" . . . . . . . . . . . . . . . . . . .   3
   6.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security considerations . . . . . . . . . . . . . . . . . . .   4
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   4
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. TODO  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     11.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

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
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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3.  Capability argument

   The server must advertise 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 positional mailbox argument to a fileinto action
   delivers the message in a mailbox with the matching [RFC3501] name.

   This document adds a new tagged argument ":mailboxid".  If the
   ":mailboxid" argument is provided, the positional mailbox argument
   refers to an [I-D.ietf-extra-imap-objectid] mailboxid rather than an
   [RFC3501] name.

   If there is no mailbox with the specified ":mailboxid" then the
   action is the same as if there was no named mailbox, and
   implementations are free to make the same choices given in [RFC5228]
   Section 4.1 when the specified mailbox doesn't exist.

   The tagged argument ":mailboxid" to fileinto consumes zero additional
   tokens.

   Example:

       require "fileinto";
       require "mailboxid";

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

5.  Test ":mailboxidexists"

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

   Usage: "mailboxidexists <mailboxids: string-list>"

   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

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   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:

     require "fileinto";
     require "mailboxid";

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

6.  Formal Syntax

                  test /= ":mailboxidexists" string-list

                  tag /= ":mailboxid"

7.  Security considerations

   This document does not add any security considerations beyond those
   in [RFC5228], [RFC5490] and [I-D.ietf-extra-imap-objectid].
   Implementers are referred to the security considerations sections of
   those documents.

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.

10.  TODO

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

11.  References

11.1.  Normative References

   [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>.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
              <https://www.rfc-editor.org/info/rfc3501>.

   [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>.

   [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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   [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>.

11.2.  Informative References

   [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.

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

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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