Network Working Group B. Leiba
Internet-Draft Huawei Technologies
Updates: 3348,3501,6154 E. Iceman
(if approved) Google, Inc.
Intended status: Standards Track January 17, 2013
Expires: July 21, 2013
IMAP LIST Special-Use Attribute: \Important
draft-iceman-imap-specialuse-important-01
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, updating RFCs 3348, 3501, and 6154.
Status of this Memo
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Definition of the 'Important' Attribute . . . . . . . . . . . 3
2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.1. Creation of the IMAP LIST Special-Use Attributes Registry . . 4
4.2. Initial entries for the registry . . . . . . . . . . . . . . 5
4.3. Instructions to the Designated Expert . . . . . . . . . . . . 6
5. Changes During Document Development . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
[RFC6154] defines an extension to the Internet Message Access
Protocol (IMAP) LIST command [RFC3501] 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. There are now three RFCs that define
mailbox attributes, and no registry for those attributes.
This document 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. This
document also creates a registry for IMAP mailbox attributes and
registers both the new attribute and those defined earlier, updating
[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' Attribute
The "\Important" mailbox attribute is a signal that the mailbox
contains messages that are likely important to the user. For
example, the system might automatically put messages there 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
it might be a way for users to train the system as to what messages
are important (the system can learn patterns from the messages the
user copies to that mailbox).
[[anchor4: Possible change here: Cyrus has suggested (1) removal of
the last sentence above, about learning, and (2) definition of an
$Important message keyword, and reference to \Important as a virtual
mailbox to collect all such messages (as \Flagged does).]]
This is distinct from the "\Flagged" attribute in that evaluation of
importance here is based on heuristics, whereas "\Flagged" is
typically based on the setting of the IMAP flag of the same name.
2.1. Formal Syntax
The following syntax specification updates the one in [RFC6154],
Section 6, using Augmented Backus-Naur Form (ABNF) as described in
[RFC5234].
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use-attr =/ "\Important"
2.2. 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
3. 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 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.
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.
4. IANA Considerations
[[RFC Editor: Please replace "THIS RFC" throughout this section with
the identification given to this document, and remove this
paragraph.]]
4.1. Creation of the IMAP LIST Special-Use Attributes Registry
IANA is asked to create a new registry in the group "Internet Message
Access Protocol (IMAP) 4 Registries". 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 4.
The registry entries will contain three fields:
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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 ("\").
New registrations will be accepted through the Expert Review policy
[RFC5226] (and see Section 4.3). New registrations are requested
through the IANA Considerations section in an RFC, or, for requests
that do not come from an RFC, by sending email to IANA asking for a
new IMAP Mailbox Name Attribute and giving the requested values for
each of the three fields.
4.2. Initial entries for the 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] |
+===============+===================================+===========+
4.3. 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.
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5. Changes During Document Development
[[anchor11: RFC Editor: Please remove this section prior to
publication.]]
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.
6. References
6.1. 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.
6.2. Informative References
[RFC3348] Gahrns, M. and R. Cheng, "The Internet Message Action
Protocol (IMAP4) Child Mailbox Extension", RFC 3348,
July 2002.
Authors' Addresses
Barry Leiba
Huawei Technologies
Phone: +1 646 827 0648
Email: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
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Eric Iceman
Google, Inc.
Email: iceman@google.com
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