A Property Types Registry for the Authentication-Results Header Field
obsoleted by
- rfc-7601 — Message Header Field for Indicating Message Authentication Status
updates
- rfc-7001 — Message Header Field for Indicating Message Authentication Status
Extracted elements (11)
RFC 7001 originally defined a small fixed set of 'ptype' values for the Authentication-Results header field. Demand emerged to report additional types of message properties through this mechanism, motivating the creation of an extensible registry rather than continuing to enumerate values in a static specification.
For new registry entries, the Designated Expert must ensure the description adequately describes the intended use; including an example in the defining document is advised, and examples from the 'Email Authentication Methods' or 'Email Authentication Result Names' registries may also illustrate intended use.
Legal values of 'ptype' MUST be drawn from the IANA 'Email Authentication Property Types' registry. No arbitrary or unregistered ptype tokens are permitted.
When a consumer of the Authentication-Results header field encounters a 'ptype' token it does not understand, it ignores the result reported with that ptype and allows processing to continue.
The 'body' ptype indicates information extracted from the body of the message, such as an arbitrary byte string, a hash, a URI, or other content of interest. Defined in RFC 7001 Section 2.2 and carried forward as an initial registry entry.
The 'header' ptype indicates information extracted from a header field of the message, such as the value of a header field or a portion thereof. Defined in RFC 7001 Section 2.2 and carried forward as an initial registry entry.
The 'policy' ptype indicates that a local policy mechanism was applied that augments or overrides the result returned by the authentication mechanism, per RFC 7001 Section 2.3. Carried forward as an initial registry entry.
The 'ptype' token in the Authentication-Results header field is redefined as an ABNF 'Keyword' (per RFC 5321 Section 4.1.2), indicating whether the evaluated property came from an SMTP command, a message header field, the message body, or some other property evaluated by the receiving MTA.
The 'smtp' ptype indicates information extracted from an SMTP command used to relay the message. Defined in RFC 7001 Section 2.2 and carried forward as an initial registry entry.
IANA created the 'Email Authentication Property Types' sub-registry within the existing 'Email Authentication Parameters' registry. New entries are subject to Expert Review (RFC 5226) and must supply: the ptype token (fitting the ABNF Keyword), a brief description of what information the ptype covers, and an optional (but recommended) reference to the defining document.
Legacy implementations that expect only the original fixed set of ptype tokens may respond to new tokens by either blocking delivery or ignoring the unrecognized portions of the header field. Because the semantics of an unknown ptype report are indeterminate—it could indicate authenticity, fraud, or an incomplete test—the recommendation is to ignore unknown ptypes rather than prevent delivery.