IMAP LIST Extension for Special-Use Mailboxes

Abstract

Some IMAP message stores include special-use mailboxes, such as those used to hold draft messages or sent messages. Many mail clients allow users to specify where draft or sent messages should be put, but configuring them requires that the user know which mailboxes the server has set aside for these purposes. This extension adds new optional mailbox attributes that a server may include in IMAP LIST command responses to identify special-use mailboxes to the client, easing configuration.

IMAP "$Important" Keyword and "\Important" Special-Use Attribute

“…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.…”

“…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."…”

“…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.…”

“…o Creates a registry for IMAP mailbox attributes and registers the new attribute and those defined in [RFC5258], [RFC3501], and [RFC6154].…”