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Versions: 00 01 02

Network Working Group                                           B. Leiba
Internet-Draft                                       Huawei Technologies
Updates: 3501,6154 (if approved)                               E. Iceman
Intended status: Standards Track                            Google, Inc.
Expires: October 15, 2013                                 April 15, 2013

      IMAP $Important Keyword and \Important Special-Use Attribute
               draft-iceman-imap-specialuse-important-02

Abstract

   RFC 6154 created an IMAP Special-Use LIST extension and defined an
   initial set of attributes.  This document defines a new attribute,
   "\Important", and establishes a new IANA registry for IMAP folder
   attributes, registering the attributes defined in RFCs 3348, 3501,
   and 6154.  This document also defines a new IMAP keyword,
   "$Important", and registers it in the registry defined in RFC 5788.

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
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   This Internet-Draft will expire on October 15, 2013.

Copyright Notice

   Copyright (c) 2013 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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2

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   1.1.  Conventions used in this document  . . . . . . . . . . . . .  2
   2.  Definition of the '$Important' Message Keyword . . . . . . . .  2
   3.  Definition of the 'Important' Mailbox Attribute  . . . . . . .  3
   3.1.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . .  3
   3.2.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  3
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  4
   5.1.  Registration of the $Important keyword . . . . . . . . . . .  4
   5.2.  Creation of the IMAP Mailbox Name Attributes Registry  . . .  5
   5.2.1.  Instructions to the Designated Expert  . . . . . . . . . .  5
   5.3.  Initial Entries for the IMAP Mailbox Name Attributes Registry 5
   6.  Changes During Document Development  . . . . . . . . . . . . .  6
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.1.  Normative References . . . . . . . . . . . . . . . . . . . .  7
   7.2.  Informative References . . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7

1.  Introduction

   The Internet Message Access Protocol (IMAP) specification [RFC3501]
   defines the use of message keywords, and an IMAP Keywords registry is
   created in [RFC5788].  [RFC6154] defines an extension to the IMAP
   LIST command for special-use mailboxes.  The extension allows servers
   to provide extra information (attributes) about the purpose of a
   mailbox and defines an initial set of special-use attributes.

   This document does the following:

   o  Defines a new message keyword, "$Important", to apply to messages
      that are considered important for the user, by some externally
      defined criteria.

   o  Registers the "$Important" keyword in the IMAP Keywords registry.

   o  Defines a new special-use attribute, "\Important", to designate a
      mailbox that will hold messages that are considered important for
      the user, by some externally defined criteria.

   o  Creates a registry for IMAP mailbox attributes and registers the
      new attribute and those defined in [RFC3348], [RFC3501], and
      [RFC6154].

1.1.  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.

2.  Definition of the '$Important' Message Keyword

   The "$Important" keyword is a signal that a message is likely
   important to the user.  The keyword can be set by the user, or
   automatically by the system based on available signals (such as who
   the message is from, who else the message is addressed to, evaluation
   of the subject or content, or other heuristics).

   This is distinct from the "\Flagged" system flag in two ways:

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   1.  "$Important" carries a specific meaning of importance, as opposed
       to urgency.  It is meant to be used for a form of triage, with
       "\Flagged" remaining as a designation of special attention or
       particular urgency.

   2.  The setting of "$Important" is expected to be based at least
       partly on heuristics, whereas "\Flagged" is intended to be set by
       the user.

3.  Definition of the 'Important' Mailbox Attribute

   The "\Important" mailbox attribute is a signal that the mailbox
   contains messages that are likely important to the user.  In an
   implementation that also supports the "$Important" keyword, this
   special use is likely to represent a virtual mailbox collecting
   messages (from other mailboxes) that are marked with the "$Important"
   keyword.  In other implementations, the system might automatically
   put messages there based on the same sorts of heuristics that are
   noted for the "$Important" keyword (see Section 2).  The distinction
   between "\Important" and "\Flagged" for mailboxes is similar to those
   between "$Important" and "\Flagged" for messages.

3.1.  Formal Syntax

   The following syntax specification adds to the one in [RFC6154],
   Section 6, using Augmented Backus-Naur Form (ABNF) as described in
   [RFC5234].

    use-attr      =/  "\Important"

3.2.  Example

   In the following example, the mailbox called "Important Messages" is
   the one designated with the "\Important" attribute.

    C: t1 list "" "Imp*"
    S: * LIST (\HasNoChildren \Important) "/" "Important Messages"
    S: * LIST (\HasNoChildren) "/" "Imported Wine"
    S: t1 OK Success

4.  Security Considerations

   The security considerations in [RFC6154], Section 7, apply equally to
   this extension.  In particular, "Conveying special-use information to
   a client exposes a small bit of extra information that could be of
   value to an attacker."  Moreover, identifying "important" messages or
   a place where important messages are kept could give an attacker a
   strategic starting point.  If the algorithm by which messages are
   determined to be important is well known, still more information is
   exposed -- perhaps, for example, there is an implication that the
   senders of these messages are particularly significant to the mailbox
   owner, and perhaps that is information that should not be made
   public.

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   As noted in RFC 6154, it is wise to protect the IMAP channel from
   passive eavesdropping, and to defend against unauthorized discernment
   of the identity of a user's "\Important" mailbox or of a user's
   "$Important" messages.

5.  IANA Considerations

   This document contains 3 actions for IANA, specified in the sections
   below:

   1.  Registration of the "$Important" keyword.

   2.  Creation of a new "IMAP Mailbox Name Attributes" registry.

   3.  Registration of initial entries in the "IMAP Mailbox Name
       Attributes" registry.

5.1.  Registration of the $Important keyword

   IANA is asked to register the $Important keyword in the "IMAP
   Keywords" registry, as follows, using the template in [RFC5788].

   IMAP keyword name: $Important

   Purpose (description): The "$Important" keyword is a signal that a
         message is likely important to the user.

   Private or Shared on a server: PRIVATE

   Is it an advisory keyword or may it cause an automatic action: Adviso
         ry (but see the reference for details).

   When/by whom the keyword is set/cleared: The keyword can be set by
         the user, or automatically by the system based on available
         signals (such as who the message is from, who else the message
         is addressed to, evaluation of the subject or content, or other
         heuristics).

   Related keywords: None (but see the reference for the related mailbox
         name attribute).

   Related IMAP capabilities: None.

   Security considerations: See [[THIS RFC]], Section 4

   Published specification: [[THIS RFC]]

   Person & email address to contact for further information: IETF Appli
         cations Area <apps-discuss@ietf.org>

   Intended usage: COMMON

   Owner/Change controller: IESG

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   Note: None.

5.2.  Creation of the IMAP Mailbox Name Attributes Registry

   IANA is asked to create a new registry in the group "Internet Message
   Access Protocol (IMAP)".  The new registry will be called "IMAP
   Mailbox Name Attributes", and will have two references: "RFC 3501,
   Section 7.2.2", and "[[THIS RFC]], Section 5".

   The registry entries will contain three fields:

   1.  Attribute Name

   2.  Description

   3.  Reference

   IANA will keep this list in alphabetical order by Attribute Name,
   which is registered without the initial backslash ("\").

   The registration policy for the new registry will be listed as "IETF
   Review or Expert Review" [RFC5226], and new registrations will be
   accepted in one of two ways:

   1.  For registrations requested in an IETF consensus document, the
       registration policy will be IETF Review, and the request will be
       made in the IANA Considerations section of the document, giving
       the requested values for each of the three fields.

   2.  For other registrations, the policy will be Expert Review policy
       (see Section 5.2.1), and the request will be made by sending
       email to IANA asking for a new IMAP Mailbox Name Attribute and
       giving the requested values for each of the three fields.

5.2.1.  Instructions to the Designated Expert

   The expert reviewer, who will be designated by the IESG, is expected
   to provide only a general review of the requested registration,
   checking that the reference and description are adequate for
   understanding the intent of the registered attribute.  Efforts should
   also be made to generalize the intent of an attribute so that
   multiple implementations with the same requirements may reuse
   existing attributes.  Except for this check, this is intended to be
   very close to a first come first served policy, and the expert should
   not block serious registration requests with a reasonable reference.
   The reference may be to any form of documentation, including a web
   page, but consideration should be given to providing one that is
   expected to be long-lived and stable.

5.3.  Initial Entries for the IMAP Mailbox Name Attributes Registry

   The registry will initially contain these entries:


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   +===============+===================================+===========+
   | Attribute     | Description                       | Reference |
   | Name          |                                   |           |
   +===============+===================================+===========+
   | All           | All messages                      | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Archive       | Archived messages                 | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Drafts        | Messages that are working drafts  | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Flagged       | Messages with the \Flagged flag   | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | HasChildren   | Has accessible child mailboxes    | [RFC3348] |
   +---------------+-----------------------------------+-----------+
   | HasNoChildren | Has no accessible child mailboxes | [RFC3348] |
   +---------------+-----------------------------------+-----------+
   | Important     | Messages deemed important to user | THIS RFC  |
   +---------------+-----------------------------------+-----------+
   | Junk          | Messages identified as Spam/Junk  | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Marked        | Server has marked the mailbox as  | [RFC3501] |
   |               | "interesting"                     |           |
   +---------------+-----------------------------------+-----------+
   | NoInferiors   | No hierarchy under this name      | [RFC3501] |
   +---------------+-----------------------------------+-----------+
   | Noselect      | The mailbox is not selectable     | [RFC3501] |
   +---------------+-----------------------------------+-----------+
   | Sent          | Sent mail                         | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Trash         | Messages the user has discarded   | [RFC6154] |
   +---------------+-----------------------------------+-----------+
   | Unmarked      | No new messages since last select | [RFC3501] |
   +===============+===================================+===========+

6.  Changes During Document Development

   [[RFC Editor: Please remove this section prior to publication.]]

   Changes in -02

   o  Added the definition and registration of $Important.

   o  Noted that \Important might be implemented as a virtual collection
      of $Important messages.

   Changes in -01

   o  Expanded the new registry to all mailbox name attributes, and
      added the attributes from 3501 and 3348 (suggested by Alexey).
      This also adds those two documents to the "updates" list.

   o  Recorded Cyrus's suggestion to define $Important.


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7.  References

7.1.  Normative References

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC6154]  Leiba, B. and J. Nicolson, "IMAP LIST Extension for
              Special-Use Mailboxes", RFC 6154, March 2011.

7.2.  Informative References

   [RFC3348]  Gahrns, M. and R. Cheng, "The Internet Message Action
              Protocol (IMAP4) Child Mailbox Extension", RFC 3348, July
              2002.

   [RFC5788]  Melnikov, A. and D. Cridland, "IMAP4 Keyword Registry",
              RFC 5788, March 2010.

Authors' Addresses

   Barry Leiba
   Huawei Technologies

   Phone: +1 646 827 0648
   Email: barryleiba@computer.org
   URI:   http://internetmessagingtechnology.org/


   Eric Iceman
   Google, Inc.

   Email: iceman@google.com













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