IMAP LIST Special-Use Attribute: \Important

defines an extension to the Internet Message Access Protocol (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. RFC 6154 did not define a 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 special-use mailbox attributes and registers both the new attribute and the initial set, updating RFC 6154.

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.

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). 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.

The following syntax specification updates the one in , Section 6, using Augmented Backus-Naur Form (ABNF) as described in .

use-attr =/ "\Important"

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

The security considerations in , 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.

[[RFC Editor: Please replace "THIS RFC" throughout this section with the identification given to this document, and remove this paragraph.]]

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 LIST Special-Use Attributes", and will have as its reference RFC 6154 and THIS RFC. New registrations will be accepted through the Expert Review policy (and see ). The registry entries will contain three fields: Attribute Name Description Reference IANA will keep this list in alphabetical order by Attribute Name, which is registered without the initial backslash ("\").

The registry will initially consist of:

+-----------+-----------------------------------+-----------+ | Attribute | Description | Reference | +-----------+-----------------------------------+-----------+ | All | All messages | [RFC6154] | +-----------+-----------------------------------+-----------+ | Archive | Archived messages | [RFC6154] | +-----------+-----------------------------------+-----------+ | Drafts | Messages that are working drafts | [RFC6154] | +-----------+-----------------------------------+-----------+ | Flagged | Messages with the \Flagged flag | [RFC6154] | +-----------+-----------------------------------+-----------+ | Important | Messages deemed important to user | THIS RFC | +-----------+-----------------------------------+-----------+ | Junk | Messages identified as Spam/Junk | [RFC6154] | +-----------+-----------------------------------+-----------+ | Sent | Sent mail | [RFC6154] | +-----------+-----------------------------------+-----------+ | Trash | Messages the user has discarded | [RFC6154] | +-----------+-----------------------------------+-----------+

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.