RFC 7410

A Property Types Registry for the Authentication-Results Header Field

📅 published December 2014, from ietf

A Property Types Registry for the Authentication-Results Header Field ✨

okay bestie, let's get the paperwork out of the way first 📋💖

Publisher: Internet Engineering Task Force (IETF) 🎀
RFC number: 7410
Authors: M. Kucherawy (Murray S. Kucherawy, 270 Upland Drive, San Francisco, CA 94127, United States) 🧚
Date: December 2014 🌸
Category: Standards Track 👑
ISSN: 2070-1721
Updates: RFC 7001 🦋
Obsoletes: no Obsoletes line in the header, so nothing gets obsoleted here 🙈

Abstract 💖

so this doc updates RFC 7001 and makes a registry for property types in the Authentication-Results header field, the one used in email authentication work. before this, people were stuck with a tiny fixed set of values. now there's a registry where new ones can be listed ✨

Status of This Memo 📜

This is an Internet Standards Track document. 💅

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7410. 🔗

Copyright Notice ⚖️

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. please review these carefully, because they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they are provided without warranty as described in the Simplified BSD License. 📝

Table of Contents 🗂️

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
2.  Updated "ptype" Definition  . . . . . . . . . . . . . . . . .   2
3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1. Introduction ✨

[RFC7001] defines the email Authentication-Results header field, which presents the results of an authentication effort in a machine-readable format. the header field creates a place to collect the output from authentication processes that are separate from the later processes that might use that output, like analysis, filtering, or sorting mechanisms. it's giving organized 🗃️

the spec in that document listed a small set of types of properties that can be reported using this mechanism. people have started wanting to report other types of properties about a message through this mechanism, and that's where this doc comes in 🙌 so this document updates the spec to allow additional property types ("ptypes") beyond the original set. it also creates a registry where new ones can be listed and their defining documents referenced. main character energy 👑

2. Updated "ptype" Definition 🦋

Advanced Backus Naur Form (ABNF) is defined in [RFC5234]. ✍️

The ABNF in Section 2.2 of [RFC7001] is updated as follows:

    ptype = Keyword
          ; indicates whether the property being evaluated was
          ; a parameter to an [SMTP] command, was a value taken
          ; from a message header field, was some property of
          ; the message body, or was some other property evaluated by
          ; the receiving Message Transfer Agent (MTA)

The ABNF token "Keyword" is defined in Section 4.1.2 of [RFC5321]. 🧩

Legal values of "ptype" are as defined in the IANA "Email Authentication Property Types" registry (see Section 3). The initial values are as follows, matching those defined in [RFC7001]:

body: info that was pulled from the body of the message. this could be an arbitrary string of bytes, a hash of a string of bytes, a Uniform Resource Identifier, or some other content of interest 👀
header: info that was pulled from the header of the message. this could be the value of a header field or some portion of a header field 📨
policy: a local policy mechanism was applied that augments or overrides the result returned by the authentication mechanism. see Section 2.3 of [RFC7001] 🛡️
smtp: info that was pulled from an SMTP command that was used to relay the message 📮

when a consumer of this header field runs into a "ptype" it doesn't understand, it ignores the result reported with that "ptype". 🙈

3. IANA Considerations 📚

IANA has created the "Email Authentication Property Types" sub-registry within the existing "Email Authentication Parameters" registry. Entries in this registry are subject to the Expert Review rules described in [RFC5226]. Each entry in the registry requires the following values:

The "ptype" token to be registered, which must fit within the ABNF described in Section 2.
A brief description of what sort of information this "ptype" is meant to cover.
An optional reference to the defining document. This is recommended, but not required.

The initial entries in this table are as follows, taken from [RFC7001]:

+--------+-------------+----------------------------------------+
| ptype  | Definition  | Description                            |
+--------+-------------+----------------------------------------+
| body   | RFC 7001    | The property being reported was found  |
|        | Section 2.2 | in the body of the message.            |
+--------+-------------+----------------------------------------+
| header | RFC 7001    | The property being reported was found  |
|        | Section 2.2 | in a header field of the message.      |
+--------+-------------+----------------------------------------+
| policy | RFC 7001    | The property being reported relates to |
|        | Section 2.3 | a locally defined policy.              |
+--------+-------------+----------------------------------------+
| smtp   | RFC 7001    | The property being reported is a       |
|        | Section 2.2 | parameter to an SMTP command used to   |
|        |             | relay the message.                     |
+--------+-------------+----------------------------------------+

For new entries, the Designated Expert needs to make sure the description provided for the new entry adequately describes the intended use. an example would be super helpful to include in the entry's defining document, if there is one. entries in the "Email Authentication Methods" registry or the "Email Authentication Result Names" registry might also work as examples of intended use 💅

4. Security Considerations 🔒

It is unknown how legacy code, which expects one of a fixed set of "ptype" tokens, will handle new tokens as they begin to appear. there are typically two options: prevent delivery of the message, or ignore those portions of the field that use unknown "ptype" tokens and allow processing of the message to continue. this part is a real issue, bestie 😭

The choice comes down to whether the consumer considers it a threat when unknown "ptypes" are present. The semantics of the report are unknown. the report might be indicating the message is authentic, fraudulent, or that a test failed to complete. The report itself is not actionable because it cannot be understood, and only its presence is certain.

⚠️ it's giving "unknown and possibly scary" 💀 the report could mean something totally different from what you'd expect, so be careful about acting on it.

Generally, the advice in this situation is to ignore unknown "ptypes". It is anticipated that a new property type evaluated by earlier handling agents would also result in the filtering of messages by those agents until consumers can be updated to interpret them. 🧱

5. Normative References 📖

[RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
           IANA Considerations Section in RFCs", BCP 26, RFC 5226,
           May 2008, <http://www.rfc-editor.org/info/rfc5226>.

[RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
           Specifications: ABNF", STD 68, RFC 5234, January 2008,
           <http://www.rfc-editor.org/info/rfc5234>.

[RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
           October 2008, <http://www.rfc-editor.org/info/rfc5321>.

[RFC7001]  Kucherawy, M., "Message Header Field for Indicating
           Message Authentication Status", RFC 7001, September 2013,
           <http://www.rfc-editor.org/info/rfc7001>.

Acknowledgements 🫶

The author wants to thank the following people for reviewing this update and giving constructive criticism: Dave Crocker, Tim Draegen, Scott Kitterman, and Franck Martin. you're all iconic 🌈

Author's Address 🧚

Murray S. Kucherawy
270 Upland Drive
San Francisco, CA  94127
United States

EMail: superuser@gmail.com

📦 where this page comes from

ietf: rfc7410 2014-12
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms