Internet DRAFT - draft-ietf-extra-specialuse-important
draft-ietf-extra-specialuse-important
Network Working Group B. Leiba, Ed.
Internet-Draft Huawei Technologies
Intended status: Standards Track June 07, 2018
Expires: December 07, 2018
IMAP $Important Keyword and \Important Special-Use Attribute
draft-ietf-extra-specialuse-important-04
Abstract
RFC 6154 created an IMAP Special-Use LIST extension and defined an
initial set of attributes. This document defines a new attribute,
"\Important", and establishes a new IANA registry for IMAP folder
attributes, registering the attributes defined in RFCs 5258, 3501,
and 6154. This document also defines a new IMAP keyword,
"$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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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 December 07, 2018.
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 (http://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . . 2
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2. Definition of the '$Important' Message Keyword . . . . . . . . 2
3. Definition of the 'Important' Mailbox Attribute . . . . . . . 3
3.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2.1. Example of a LIST Response . . . . . . . . . . . . . . . . 3
3.2.2. Examples of Creating a New Mailbox using \Important . . . 4
4. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6.1. Registration of the $Important keyword . . . . . . . . . . . 5
6.2. Creation of the IMAP Mailbox Name Attributes Registry . . . 6
6.2.1. Instructions to the Designated Expert . . . . . . . . . . 7
6.3. Initial Entries for the IMAP Mailbox Name Attributes Registry 7
7. Changes During Document Development . . . . . . . . . . . . . 8
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Internet Message Access Protocol (IMAP) specification [RFC3501]
defines the use of message keywords, and an IMAP Keywords registry is
created in [RFC5788]. [RFC6154] defines an extension to the IMAP
LIST command for special-use mailboxes. The extension allows servers
to provide extra information (attributes) about the purpose of a
mailbox and defines an initial set of special-use attributes.
This document does the following:
o Defines a new message keyword, "$Important", to apply to messages
that are considered important for the user, by some externally
defined criteria.
o Registers the "$Important" keyword in the IMAP Keywords registry.
o Defines a new special-use attribute, "\Important", to designate a
mailbox that will hold messages that are considered important for
the user, by some externally defined criteria.
o Creates a registry for IMAP mailbox attributes and registers the
new attribute and those defined in [RFC5258], [RFC3501], and
[RFC6154].
1.1. Conventions used in this document
In examples, "C:" indicates lines sent by a client that is connected
to a server. "S:" indicates lines sent by the server to the client.
2. Definition of the '$Important' Message Keyword
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The "$Important" keyword is a signal that a message is likely
important to the user. The keyword is generally expected to be set
automatically by the system based on available signals (such as who
the message is from, who else the message is addressed to, evaluation
of the subject or content, or other heuristics). While the keyword
also can be set by the user, that is not expected to be the primary
usage.
This is distinct from the "\Flagged" system flag in two ways:
1. "$Important" carries a meaning of general importance, as opposed
to follow-up or urgency. It is meant to be used for a form of
triage, with "\Flagged" remaining as a designation of special
attention, need for follow-up, or time-sensitivity. In
particular, the sense of "$Important" is that other messages that
are "like this one" according to some server-applied heuristics
will also be $Important.
2. The setting of "$Important" is expected to be based at least
partly on heuristics, generally set automatically by the server,
whereas "\Flagged" is only intended to be set by the user with
some sort of "flag this message" or "put a star on this message"
interface.
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]. Be sure to see the ABNF notes at the beginning of
[RFC3501], Section 9.
use-attr =/ "\Important"
3.2. Examples
3.2.1. Example of a LIST Response
In the following example, the mailbox called "Important Messages" is
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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
3.2.2. Examples of Creating a New Mailbox using \Important
In the following example, the mailbox called "Important Messages" is
created with the "\Important" attribute on a server that advertises
the "CREATE-SPECIAL-USE" capability string.
C: t1 CREATE "Important Messages" (USE (\Important))
S: t1 OK Mailbox created
The following example is similar to the previous one, but the server
is not able to assign the \Important attribute to the new mailbox.
C: t1 CREATE "Important Messages" (USE (\Important))
S: t1 NO [USEATTR] Not created; an \Important mailbox already exists
The following example is similar to the previous one, but the server
does not support this extension.
C: t1 CREATE "Important Messages" (USE (\Important))
S: t1 NO [USEATTR] Mailbox not created; unsupported use \Important
In both of the failure-mode examples, the "USEATTR" response code
lets the client know that the problem is in the "USE" parameters.
Note that the same response code is given in both cases, and the
human-readable text is the only way to tell the difference. That
text is not parsable by the client (it can only be logged and/or
reported to the user).
4. Implementation Notes
This section is non-normative and is intended to describe the
intended (and current as of this publication) usage of "$Important"
in contrast with "\Flagged" on a message.
On the server:
o \Flagged is set or cleared in response to an explicit command from
the client.
o $Important is set via a heuristic process performed by the server,
usually involving analysis of header fields, what mailbox the
message is filed in, perhaps message content, attachments, and
such. It may then be set or cleared in response to an explicit
command from the client, and the server may use that to adjust the
heuristics in the future. It's also possible that the server will
re-evaluate this and make a message $Important later if the user
accesses the message frequently, for example.
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On the client:
o Typically, an icon such as a flag or a star, or an indication such
as red or bold text, is associated with \Flagged, and the UI
provides a way for the user to turn that icon or indication on or
off. Manipulation of the this results in a command to the server.
o Typically, a lesser indication is used for $Important. The client
might or might not provide the user with a way to manipulate it.
If it does, manipulation results in a command to the server.
5. Security Considerations
The security considerations in [RFC6154], Section 7, apply equally to
this extension. In particular, "Conveying special-use information to
a client exposes a small bit of extra information that could be of
value to an attacker." Moreover, identifying "important" messages or
a place where important messages are kept could give an attacker a
strategic starting point. If the algorithm by which messages are
determined to be important is well known, still more information is
exposed -- perhaps, for example, there is an implication that the
senders of these messages are particularly significant to the mailbox
owner, and perhaps that is information that should not be made
public.
As noted in RFC 6154, it is wise to protect the IMAP channel from
passive eavesdropping, and to defend against unauthorized discernment
of the identity of a user's "\Important" mailbox or of a user's
"$Important" messages. See [RFC3501], Section 11, for security
considerations about using the IMAP STARTTLS command to protect the
IMAP channel.
6. 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.
6.1. 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: $Important
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Purpose (description): The "$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:
Advisory (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 5
Published specification: [[THIS RFC]]
Person & email address to contact for further information:
IETF Applications and Real-Time Area <art@ietf.org>
Intended usage: COMMON
Owner/Change controller: IESG
Note: None.
6.2. 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 6". This registry will be
shared with the JSON Meta Application Protocol (JMAP) for Mail [I-D
.ietf-jmap-mail].
The registry entries will contain the following fields:
1. Attribute Name
2. Description
3. Reference
4. Usage Notes
IANA will keep this list in alphabetical order by Attribute Name,
which is registered without the initial backslash ("\"). The names
are generally registered with initial capital letters, but are
treated as case-insensitive US-ASCII strings.
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The "Usage Notes" field is free-form US-ASCII text that will normally
be empty (and is empty if it's not specified in the registration
request). It is intended to hold things such as "not used by JMAP"
and "JMAP only". The field is for human use, and there is no need
for a registry of strings that may appear here.
The registration policy for the new registry will be listed as "IETF
Review or Expert Review" [RFC8126], 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 fields.
2. For other registrations, the policy will be Expert Review policy
(see Section 6.2.1), 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 fields. While a
formal specification is not required, the reference document
should provide a description of the proposed attribute sufficient
for building interoperable implementations. An Informational RFC
(submitted through the IETF or Independent stream) is a fine way
to publish a reference document (see also Section 6.2.1).
6.2.1. 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.
6.3. 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 | [RFC5258] | *
+---------------+-----------------------------------+-----------+
| HasNoChildren | Has no accessible child mailboxes | [RFC5258] | *
+---------------+-----------------------------------+-----------+
| 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] | *
+---------------+-----------------------------------+-----------+
| NonExistent | The mailbox name doesn't actually | [RFC5258] | *
| | exist | |
+---------------+-----------------------------------+-----------+
| Noselect | The mailbox is not selectable | [RFC3501] | *
+---------------+-----------------------------------+-----------+
| Remote | The mailbox exists on a remote | [RFC5258] | *
| | server | |
+---------------+-----------------------------------+-----------+
| Sent | Sent mail | [RFC6154] |
+---------------+-----------------------------------+-----------+
| Subscribed | The mailbox is subscribed to | [RFC5258] |
+---------------+-----------------------------------+-----------+
| Trash | Messages the user has discarded | [RFC6154] |
+---------------+-----------------------------------+-----------+
| Unmarked | No new messages since last select | [RFC3501] | *
+===============+===================================+===========+
The rows marked with "*" at the end should have their Usage Notes
field set to "not used by JMAP".
7. Changes During Document Development
[[RFC Editor: Please remove this section prior to publication.]]
Changes in draft-ietf-extra-specialuse-important-00
o Removed "specific" from "a specific meaning of general importance"
because it sounded stupid.
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o Added a "Usage Notes" column to the registry table in 6.2, and
called out some "not used by JMAP" in 6.3.
Changes in draft-leiba-extra-specialuse-important-01
o Updated "IETF Applications Area" to "IETF Applications and Real-
Time Area".
o Changed some wording to make the distinction between \Flagged and
\Important clearer.
o Added some text explaining how \Important is used in existing
servers.
o Added a note in the ABNF section referring to the ABNF notes in
the IMAP spec.
Changes in draft-leiba-extra-specialuse-important-00
o Reset status, moved Eric to "Contributors", changed Barry to
"Editor"
o Updated BCP 26 reference to RFC 8126.
Changes in draft-iceman-imap-specialuse-important-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 draft-iceman-imap-specialuse-important-01
o Expanded the new registry to all mailbox name attributes, and
added the attributes from 3501 and 5258 (suggested by Alexey).
This also adds those two documents to the "updates" list.
o Recorded Cyrus's suggestion to define $Important.
8. Contributors
The following author was an original contributor to this document in
addition to the editor.
Eric "Iceman"
Google
iceman@google.com
9. References
9.1. Normative References
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[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[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.
[RFC8126] Cotton, M., Leiba, B. and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www
.rfc-editor.org/info/rfc8126>.
9.2. Informative References
[I-D.ietf-jmap-mail]
Jenkins, N., "JMAP for Mail", Internet-Draft draft-ietf-
jmap-mail-04, March 2018.
[RFC5258] Leiba, B. and A. Melnikov, "Internet Message Access
Protocol version 4 - LIST Command Extensions", RFC 5258,
DOI 10.17487/RFC5258, June 2008, <https://www.rfc-
editor.org/info/rfc5258>.
[RFC5788] Melnikov, A. and D. Cridland, "IMAP4 Keyword Registry",
RFC 5788, March 2010.
Author's Address
Barry Leiba, editor
Huawei Technologies
Phone: +1 646 827 0648
Email: barryleiba@computer.org
URI: http://internetmessagingtechnology.org/
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