IMAP4 Keyword Registry
updated by
- rfc-8621 — The JSON Meta Application Protocol (JMAP) for Mail
Extracted elements (21)
The Expert Reviewer MAY upgrade a 'limited use' registration to 'common use', or downgrade a 'common use' registration to 'limited use'. This flexibility allows the reviewer to match the registration level to the actual deployment reality of a keyword.
The registry was created because different IMAP client implementors used keywords with different names for the same semantics (or the same names with different semantics), causing interoperability problems. The '$' prefix for common-use keywords is introduced to signal standardized semantics.
When an IMAP keyword being registered is already deployed, Expert Reviewers should favor registering it over requiring perfect documentation or requesting a name change. This pragmatic policy recognizes the value of capturing de-facto standards even if imperfectly documented.
Some IMAP server implementors already map equivalent keywords automatically to improve cross-client interoperability. The registry is intended to reduce the need for such ad-hoc server-side mapping by establishing authoritative keyword names.
IMAP keyword registrations MUST NOT be deleted; keywords no longer appropriate for use can be declared DEPRECATED by a change to their 'intended usage' field.
IMAP keywords intended for 'common use' SHOULD be standardized in IETF Review documents. Note that IETF Review documents still require Expert Review.
Keywords intended for 'common use' SHOULD start with the '$' prefix. This is a SHOULD rather than MUST because some widely deployed IMAP keywords in common use predate this convention.
Once the $Forwarded keyword is set on a message, the flag SHOULD NOT be cleared. There is no mechanism to detect whether a message was forwarded more than once.
Once the $MDNSent keyword is set (indicating an MDN was sent or a message was uploaded as sent/draft), the flag SHOULD NOT be cleared.
Registration of an IMAP keyword requires Expert Review per RFC 5226. The registration request must be posted to the Message Organization WG mailing list and CC'd to IANA, with at least two weeks allowed for community input before the expert decides.
The Expert Reviewer SHOULD refuse a 'limited use' registration if there is an already registered IMAP keyword that serves the same purpose but has a different name, to prevent duplicate registrations.
The Expert Reviewer should take no longer than six weeks to make and announce a decision, or notify the mailing list that more time is required. Decisions can be appealed to Application Area Directors and then to the full IESG.
The Owner/Change controller field MUST be 'IESG' for any 'common use' keyword registration specified in an IETF Review document. When the controller is not a Standardization Organization, the registration MUST clarify whether it is controlled by a company or individual.
IMAP keywords are boolean named flags defined in RFC 3501 that clients use to annotate messages in an IMAP mailbox. They are optional per the IMAP specification but supported by the majority of IMAP servers.
The $Forwarded keyword (BOTH private and shared, COMMON use) indicates the message was resent to another email address. It is advisory and typically used to display a different icon for forwarded messages.
The $MDNSent keyword (SHARED, COMMON use) specifies that a Message Disposition Notification must not be sent for the annotated message. It is set when a client acts on an MDN request or uploads a sent/draft message, and can also be set by a delivery agent.
The $SubmitPending keyword (SHARED, COMMON use) designates a message as awaiting submission. When both $SubmitPending and $Submitted are set simultaneously, the message is being actively submitted.
The $Submitted keyword (SHARED, COMMON use) designates the message as being sent out. When both $Submitted and $SubmitPending are set, the message is being actively submitted. It can trigger automatic client action.
This document establishes the 'IMAP Keywords' IANA registry, requiring Expert Review for all registrations. Two usage tiers exist: 'common use' (expected in at least two independent client implementations) and 'limited use' (vendor- or organization-specific).
A server implementing $Forwarded as a shared keyword may disclose that a confidential message was forwarded. Similarly, servers implementing $SubmitPending or $Submitted as shared keywords may disclose that a confidential message is scheduled to be or is actively being sent.
IMAP keywords are a base IMAP feature and this document does not change their behavior, so no new security issues are introduced at the protocol level. Security considerations specific to individual keywords are documented in each keyword's registration template.