Internet Engineering Task Force (IETF)                      M. Kucherawy
Request for Comments: 8601                                      May 2019
Obsoletes: 7601
Category: Standards Track
ISSN: 2070-1721

Message Header Field for Indicating Message Authentication Status




This document specifies a message header field called "Authentication-Results" for use with electronic mail messages to indicate the results of message authentication efforts. Any receiver-side software, such as mail filters or Mail User Agents (MUAs), can use this header field to relay that information in a convenient and meaningful way to users or to make sorting and filtering decisions.


This document obsoletes RFC 7601.

このドキュメントはRFC 7601を廃止します。

Status of This Memo


This is an Internet Standards Track document.

これはInternet Standards Trackドキュメントです。

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 7841.

このドキュメントは、IETF(Internet Engineering Task Force)の製品です。これは、IETFコミュニティのコンセンサスを表しています。公開レビューを受け、インターネットエンジニアリングステアリンググループ(IESG)による公開が承認されました。インターネット標準の詳細については、RFC 7841のセクション2をご覧ください。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

Copyright(c)2019 IETF Trustおよびドキュメントの作成者として識別された人物。全著作権所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as 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 are provided without warranty as described in the Simplified BSD License.

この文書は、BCP 78およびIETF文書に関するIETFトラストの法的規定(の対象であり、この文書の発行日に有効です。これらのドキュメントは、このドキュメントに関するあなたの権利と制限を説明しているため、注意深く確認してください。このドキュメントから抽出されたコードコンポーネントには、Trust Legal Provisionsのセクション4.eに記載されているSimplified BSD Licenseテキストが含まれている必要があり、Simplified BSD Licenseに記載されているように保証なしで提供されます。

Table of Contents


   1. Introduction ....................................................4
      1.1. Purpose ....................................................5
      1.2. Trust Boundary .............................................6
      1.3. Processing Scope ...........................................7
      1.4. Requirements ...............................................7
      1.5. Definitions ................................................7
           1.5.1. Key Words ...........................................7
           1.5.2. Internationalized Email .............................7
           1.5.3. Security ............................................8
           1.5.4. Email Architecture ..................................8
           1.5.5. Other Terms .........................................9
      1.6. Trust Environment .........................................10
   2. Definition and Format of the Header Field ......................10
      2.1. General Description .......................................10
      2.2. Formal Definition .........................................11
      2.3. Property Types (ptypes) and Properties ....................13
      2.4. The "policy" ptype ........................................15
      2.5. Authentication Service Identifier Field ...................15
      2.6. Version Tokens ............................................17
      2.7. Defined Methods and Result Values .........................17
           2.7.1. DKIM ...............................................17
           2.7.2. SPF ................................................19
           2.7.3. "iprev" ............................................20
           2.7.4. SMTP AUTH ..........................................21
           2.7.5. Other Registered Codes .............................22
           2.7.6. Extension Methods ..................................22
           2.7.7. Extension Result Codes .............................23
   3. The "iprev" Authentication Method ..............................23
   4. Adding the Header Field to a Message ...........................25
      4.1. Header Field Position and Interpretation ..................26
      4.2. Local Policy Enforcement ..................................27
   5. Removing Existing Header Fields ................................28
   6. IANA Considerations ............................................29
      6.1. The Authentication-Results Header Field ...................29
      6.2. "Email Authentication Methods" Registry Description .......30
      6.3. "Email Authentication Methods" Registry Update ............31
           6.3.1. "header.a" for DKIM ................................32
           6.3.2. "header.s" for DKIM ................................32
      6.4. "Email Authentication Property Types" Registry
           Description ...............................................32
      6.5. "Email Authentication Property Types" Registry Update .....33
      6.6. "Email Authentication Result Names" Registry Description ..33
      6.7. "Email Authentication Result Names" Registry Update .......34
      6.8. SMTP Enhanced Status Codes ................................34
   7. Security Considerations ........................................35
      7.1. Forged Header Fields ......................................35
      7.2. Misleading Results ........................................36
      7.3. Header Field Position .....................................37
      7.4. Reverse IP Query Denial-of-Service Attacks ................37
      7.5. Mitigation of Backscatter .................................37
      7.6. Internal MTA Lists ........................................37
      7.7. Attacks against Authentication Methods ....................38
      7.8. Intentionally Malformed Header Fields .....................38
      7.9. Compromised Internal Hosts ................................38
      7.10. Encapsulated Instances ...................................38
      7.11. Reverse Mapping ..........................................39
   8. References .....................................................39
      8.1. Normative References ......................................39
      8.2. Informative References ....................................40
   Appendix A. Legacy MUAs ...........................................44
   Appendix B. Authentication-Results Examples .......................44
     B.1. Trivial Case: Header Field Not Present .....................44
     B.2. Nearly Trivial Case: Service Provided, but No
          Authentication Done ........................................45
     B.3. Service Provided, Authentication Done ......................46
     B.4. Service Provided, Several Authentications Done, Single
          MTA ........................................................47
     B.5. Service Provided, Several Authentications Done, Different
          MTAs .......................................................48
     B.6. Service Provided, Multi-tiered Authentication Done .........50
     B.7. Comment-Heavy Example ......................................51
   Appendix C. Operational Considerations about Message
               Authentication ........................................52
   Appendix D. Changes since RFC 7601 ................................53
   Acknowledgments ...................................................54
   Author's Address ..................................................54
1. Introduction
1. はじめに

This document describes a header field called "Authentication-Results" for electronic mail messages that presents the results of a message authentication effort in a machine-readable format. The intent of the header field is to create a place to collect such data when message authentication mechanisms are in use so that a Mail User Agent (MUA) and downstream filters can make filtering decisions and/or provide a recommendation to the user as to the validity of the message's origin and possibly the safety and integrity of its content.


End users are not expected to be direct consumers of this header field. This header field is intended for consumption by programs that will then use such data or render it in a human-usable form.


This document specifies the format of this header field and discusses the implications of its presence or absence. However, it does not discuss how the data contained in the header field ought to be used, such as what filtering decisions are appropriate or how an MUA might render those results, as these are local policy and/or user interface design questions that are not appropriate for this document.


At the time of publication of this document, the following are published email authentication methods:


o SMTP Service Extension for Authentication [AUTH]

o 認証用のSMTPサービス拡張[AUTH]

o DomainKeys Identified Mail Signatures [DKIM]

o DomainKeysで識別されたメール署名[DKIM]

o Domain-based Message Authentication, Reporting, and Conformance [DMARC]

o ドメインベースのメッセージ認証、レポート、および準拠[DMARC]

o Sender Policy Framework [SPF]

o 送信者ポリシーフレームワーク[SPF]

o reverse IP address name validation ("iprev", defined in Section 3)

o 逆IPアドレス名の検証(「iprev」、セクション3で定義)

o Require-Recipient-Valid-Since Header Field and SMTP Service Extension [RRVS]

o Require-Recipient-Valid-SinceヘッダーフィールドとSMTPサービス拡張[RRVS]

o S/MIME Signature Verification [SMIME-REG]

o S / MIME署名の検証[SMIME-REG]

o Vouch By Reference [VBR]

o 参照による保証[VBR]

The following Historic specifications were previously supported by this framework but have since become obsolete:


o Author Domain Signing Practices [ADSP] (Historic)

o 著者ドメイン署名の実践[ADSP](歴史的)

o DomainKeys [DOMAINKEYS] (Historic)

o DomainKeys [DOMAINKEYS](履歴)

Note that at the time of publication of this document the Sender ID specification [SENDERID] (Experimental) is no longer supported by this framework. Discussion regarding moving it to Historic status is underway.

このドキュメントの公開時点では、Sender ID仕様[SENDERID](試験的)はこのフレームワークでサポートされていません。歴史的地位への移行に関する議論が進行中です。

There exist registries for tokens used within this header field that refer to the specifications listed above. Section 6 describes the registries and their contents and specifies the process by which entries are added or updated. It also updates the existing contents to match the current states of these specifications.


The goal of this work is to give current and future authentication schemes a common framework within which to deliver their results to downstream agents and discourage the creation of unique header fields for each.


Although SPF defined a header field called "Received-SPF" and the historic DomainKeys defined one called "DomainKey-Status" for this purpose, those header fields are specific to the conveyance of their respective results only and thus are insufficient to satisfy the requirements enumerated below. In addition, many SPF implementations have adopted the header field specified here at least as an option, and DomainKeys has been obsoleted by DKIM.


1.1. Purpose
1.1. 目的

The header field defined in this document is expected to serve several purposes:


1. Convey the results of various message authentication checks, which are applied by upstream filters and Mail Transfer Agents (MTAs) and then passed to MUAs and downstream filters within the same "trust domain". Such agents might wish to render those results to end users or to use those data to apply more or less stringent content checks based on authentication results.

1. さまざまなメッセージ認証チェックの結果を伝えます。これは、アップストリームフィルターおよびメール転送エージェント(MTA)によって適用され、同じ「信頼ドメイン」内のMUAおよびダウンストリームフィルターに渡されます。このようなエージェントは、これらの結果をエンドユーザーに表示したり、これらのデータを使用して、認証結果に基づいて多少厳格なコンテンツチェックを適用したりできます。

2. Provide a common location within a message for such data.

2. そのようなデータのメッセージ内の共通の場所を提供します。

3. Create an extensible framework for reporting new authentication methods as they emerge.

3. 新しい認証方法が出現したときに報告するための拡張可能なフレームワークを作成します。

In particular, the mere presence of this header field does not mean its contents are valid. Rather, the header field is reporting assertions made by one or more authentication schemes applied somewhere upstream. For an MUA or downstream filter to treat the assertions as actually valid, there must be an assessment of the trust relationship among such agents, the validating MTA, the paths between them, and the mechanism for conveying the information.

特に、このヘッダーフィールドが存在するだけでは、その内容が有効であるとは限りません。むしろ、ヘッダーフィールドは、上流のどこかに適用された1つ以上の認証スキームによって作成されたアサーションを報告しています。 MUAまたはダウンストリームフィルターがアサーションを実際に有効であると見なすには、そのようなエージェント間の信頼関係、検証するMTA、それらの間のパス、および情報を伝達するメカニズムの評価が必要です。

1.2. Trust Boundary
1.2. 信頼境界

This document makes several references to the "trust boundary" of an Administrative Management Domain (ADMD). Given the diversity among existing mail environments, a precise definition of this term isn't possible.


Simply put, a transfer from the producer of the header field to the consumer must occur within a context that permits the consumer to treat assertions by the producer as being reliable and accurate (trustworthy). How this trust is obtained is outside the scope of this document. It is entirely a local matter.


Thus, this document defines a "trust boundary" as the delineation between "external" and "internal" entities. Services that are internal -- within the trust boundary -- are provided by the ADMD's infrastructure for its users. Those that are external are outside of the authority of the ADMD. By this definition, hosts that are within a trust boundary are subject to the ADMD's authority and policies, independent of their physical placement or their physical operation. For example, a host within a trust boundary might actually be operated by a remote service provider and reside physically within its data center.


It is possible for a message to be evaluated inside a trust boundary but then depart and re-enter the trust boundary. An example might be a forwarded message such as a message/rfc822 attachment (see "Multipurpose Internet Mail Extensions" [MIME]) or one that is part of a multipart/digest. The details reported by this field cannot be trusted in that case. Thus, if found within one of those media types, this field is typically ignored.

メッセージが信頼境界内で評価され、その後、信頼境界から出て再び入る可能性があります。たとえば、message / rfc822添付ファイル(「多目的インターネットメール拡張機能」[MIME]を参照)などの転送メッセージや、multipart / digestの一部であるメッセージなどです。この場合、このフィールドによって報告された詳細は信頼できません。したがって、これらのメディアタイプの1つで見つかった場合、このフィールドは通常無視されます。

Note that an MUA could be configured to retrieve messages from a receiver yet not be within the receiver's ADMD. In this case, for the purposes of this work, that MUA is considered to be within the receiver's ADMD if it is configured to identify and ascribe value to authentication results recorded by that ADMD.


1.3. Processing Scope
1.3. 処理範囲

The content of this header field is meant to convey to message consumers that authentication work on the message was already done within its trust boundary, and those results are being presented. It is not intended to provide message parameters to consumers so that they can perform authentication protocols on their own.


1.4. Requirements
1.4. 必要条件

This document establishes no new requirements on existing protocols, insofar as a non-participating service will continue to interoperate with the deployed messaging infrastructure.


In particular, this document establishes no requirement on MTAs to reject or filter arriving messages that do not pass authentication checks. The data conveyed by the specified header field's contents are for the information of MUAs and filters and are to be used at their discretion.


A participating ADMD does undertake some filtering and message modification obligations as described in Section 5.


1.5. Definitions
1.5. 定義

This section defines various terms used throughout this document.


1.5.1. Key Words
1.5.1. キーワード

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.


1.5.2. Internationalized Email
1.5.2. 国際化された電子メール

In this document, there are references to messages formatted to support Email Address Internationalization (EAI). Reference material for this can be found in [RFC6530], [RFC6531], and [RFC6532]. Generally speaking, these documents allow UTF-8 in most places that free-form text can be found and U-labels where domain names can be used, and this document extends Authentication-Results accordingly.


1.5.3. Security
1.5.3. 安全保障

"Guidelines for Writing RFC Text on Security Considerations" [SECURITY] discusses authentication and authorization and the conflation of the two concepts. The use of those terms within the context of recent message security work has given rise to slightly different definitions, and this document reflects those current usages, as follows:


o "Authorization" is the establishment of permission to use a resource or represent an identity. In this context, authorization indicates that a message from a particular ADMD arrived via a route the ADMD has explicitly approved.

o 「許可」とは、リソースを使用する、またはIDを表す許可の確立です。このコンテキストでは、承認は、特定のADMDからのメッセージがADMDが明示的に承認したルートを介して到着したことを示します。

o "Authentication" is the assertion of validity of a piece of data about a message (such as the sender's identity) or the message in its entirety.

o 「認証」とは、メッセージ(送信者のIDなど)またはメッセージ全体に関するデータの一部の有効性を表明することです。

As examples: SPF is an authorization mechanism in that it expresses a result that shows whether the ADMD that apparently sent the message has explicitly authorized the connecting Simple Mail Transfer Protocol (SMTP) client [SMTP] to relay messages on its behalf, but it does not actually validate any other property of the message itself. By contrast, DKIM is agnostic as to the routing of a message but uses cryptographic signatures to authenticate agents, assign (some) responsibility for the message (which implies authorization), and ensure that the listed portions of the message were not modified in transit. Since the signatures are not tied to SMTP connections, they can be added by the ADMD of origin, intermediate ADMDs (such as a mailing list server), other handling agents, or any combination of these.

例として:SPFは、メッセージを送信したように見えるADMDが、接続するSimple Mail Transfer Protocol(SMTP)クライアント[SMTP]に代わってメッセージをリレーすることを明示的に承認したかどうかを示す結果を表すという承認メカニズムですが、実際にはメッセージ自体の他のプロパティは実際には検証しません。対照的に、DKIMはメッセージのルーティングにとらわれませんが、暗号署名を使用してエージェントを認証し、メッセージに(承認を意味する)責任を割り当て、メッセージのリストされた部分が転送中に変更されていないことを確認します。署名はSMTP接続に関連付けられていないため、送信元のADMD、中間ADMD(メーリングリストサーバーなど)、他の処理エージェント、またはこれらの任意の組み合わせによって追加できます。

Rather than create a separate header field for each class of solution, this specification groups them both into a single header field.


1.5.4. Email Architecture
1.5.4. メールアーキテクチャ

o A "border MTA" is an MTA that acts as a gateway between the general Internet and the users within an organizational boundary. (See also Section 1.2.)

o 「境界MTA」は、一般的なインターネットと組織の境界内のユーザーとの間のゲートウェイとして機能するMTAです。 (セクション1.2も参照してください。)

o A "delivery MTA" (or Mail Delivery Agent or MDA) is an MTA that actually enacts delivery of a message to a user's inbox or other final delivery.

o 「配信MTA」(またはメール配信エージェントまたはMDA)は、ユーザーの受信ボックスへのメッセージの配信またはその他の最終的な配信を実際に実行するMTAです。

o An "intermediate MTA" is any MTA that is not a delivery MTA and is also not the first MTA to handle the message.

o 「中間MTA」は、配信MTAではなく、メッセージを処理する最初のMTAでもないMTAです。

o A Message Submission Agent (MSA) is an agent that accepts a message from an MUA, introducing it to the mail-handling stream.

o メッセージ送信エージェント(MSA)は、MUAからメッセージを受け取り、メール処理ストリームに導入するエージェントです。

The following diagram illustrates the flow of mail among these defined components. See "Internet Mail Architecture" [EMAIL-ARCH] for further discussion on general email system architecture, which includes detailed descriptions of these components, and Appendix C of this document for discussion about the common aspects of email authentication in current environments.


                          +-----+   +-----+   +------------+
                          | MUA |-->| MSA |-->| Border MTA |
                          +-----+   +-----+   +------------+
                                               | Internet |
   +-----+   +-----+   +------------------+   +------------+
   | MUA |<--| MDA |<--| Intermediate MTA |<--| Border MTA |
   +-----+   +-----+   +------------------+   +------------+

Generally, it is assumed that the work of applying message authentication schemes takes place at a border MTA or a delivery MTA. This specification is written with that assumption in mind. However, there are some sites at which the entire mail infrastructure consists of a single host. In such cases, such terms as "border MTA" and "delivery MTA" might well apply to the same machine or even the very same agent. It is also possible that some message authentication tests could take place on an intermediate MTA. Although this document doesn't specifically describe such cases, they are not meant to be excluded.


1.5.5. Other Terms
1.5.5. その他の条件

In this document, the term "producer" refers to any component that adds this header field to messages it is handling, and "consumer" refers to any component that identifies, extracts, and parses the header field to use as part of a handling decision.

このドキュメントでは、「プロデューサー」という用語は、処理しているメッセージにこのヘッダーフィールドを追加するコンポーネントを指し、「コンシューマー」は、処理決定の一部として使用するためにヘッダーフィールドを識別、抽出、解析するコンポーネントを指します。 。

1.6. Trust Environment
1.6. 信頼環境

This header field permits one or more message validation mechanisms to communicate output to one or more separate assessment mechanisms. These mechanisms operate within a unified trust boundary that defines an ADMD. An ADMD contains one or more entities that perform validation and generate the header field and one or more that consume it for some type of assessment. The field often contains no integrity or validation mechanism of its own, so its presence must be trusted implicitly. Hence, valid use of the header field requires removing any occurrences of it that claim to be associated with the ADMD when the message enters the ADMD. This ensures that later occurrences have been added within the trust boundary of the ADMD.

このヘッダーフィールドを使用すると、1つ以上のメッセージ検証メカニズムが1つ以上の個別の評価メカニズムに出力を伝達できます。これらのメカニズムは、ADMDを定義する統一された信頼境界内で動作します。 ADMDには、検証を実行してヘッダーフィールドを生成する1つ以上のエンティティと、特定の種類の評価のためにヘッダーフィールドを使用する1つ以上のエンティティが含まれています。多くの場合、フィールドには整合性や独自の検証メカニズムが含まれていないため、その存在は暗黙的に信頼されている必要があります。したがって、ヘッダーフィールドを有効に使用するには、メッセージがADMDに入るときにADMDに関連付けられていると主張するその出現をすべて削除する必要があります。これにより、後で発生するものがADMDの信頼境界内に確実に追加されます。

The authserv-id token defined in Section 2.2 can be used to reference an entire ADMD or a specific validation engine within an ADMD. Although the labeling scheme is left as an operational choice, some guidance for selecting a token is provided in later sections of this document.


2. Definition and Format of the Header Field
2. ヘッダーフィールドの定義と形式

This section gives a general overview of the format of the header field being defined and then provides a formal specification.


2.1. General Description
2.1. 概要

The header field specified here is called "Authentication-Results". It is a structured header field as defined in "Internet Message Format" [MAIL], and thus all of the related definitions in that document apply.


This header field is added at the top of the message as it transits MTAs that do authentication checks, so some idea of how far away the checks were done can be inferred. It is therefore considered to be a trace field as defined in [MAIL], and thus all of the related definitions in that document apply.


The value of the header field (after removing comments) consists of an authentication service identifier, an optional version, and then a series of statements and supporting data. The statements are of the form "method=result" and indicate which authentication method or methods were applied and their respective results. For each such statement, the supporting data can include a "reason" string and one or more "property=value" statements indicating which message properties were evaluated to reach that conclusion.

ヘッダーフィールドの値(コメントを削除した後)は、認証サービス識別子、オプションのバージョン、そして一連のステートメントとサポートデータで構成されます。ステートメントは「method = result」の形式であり、適用された認証方法とそれぞれの結果を示します。そのようなステートメントごとに、サポートデータには、「reason」文字列と、その結論に到達するために評価されたメッセージプロパティを示す1つ以上の「property = value」ステートメントを含めることができます。

The header field can appear more than once in a single message, more than one result can be represented in a single header field, or a combination of these can be applied.


2.2. Formal Definition
2.2. 正式な定義

Formally, the header field is specified as shown below using Augmented Backus-Naur Form [ABNF]. Examples of valid header fields with explanations of their semantics can be found in Appendix B.


authres-header-field = "Authentication-Results:" authres-payload

authres-header-field = "Authentication-Results:" authres-payload

     authres-payload = [CFWS] authserv-id
              [ CFWS authres-version ]
              ( no-result / 1*resinfo ) [CFWS] CRLF

authserv-id = value ; see below for a description of this element

authserv-id = value;この要素の説明については、以下を参照してください

     authres-version = 1*DIGIT [CFWS]
             ; indicates which version of this specification is in use;
             ; this specification is version "1", and the absence of a
             ; version implies this version of the specification
     no-result = [CFWS] ";" [CFWS] "none"
               ; the special case of "none" is used to indicate that no
               ; message authentication was performed
     resinfo = [CFWS] ";" methodspec [ CFWS reasonspec ]
               [ CFWS 1*propspec ]
     methodspec = [CFWS] method [CFWS] "=" [CFWS] result
                ; indicates which authentication method was evaluated
                ; and what its output was

reasonspec = "reason" [CFWS] "=" [CFWS] value ; a free-form comment on the reason the given result ; was returned

reasonspec = "reason" [CFWS] "=" [CFWS] value;指定された結果の理由に関する自由形式のコメント。返された

     propspec = ptype [CFWS] "." [CFWS] property [CFWS] "=" pvalue
              ; an indication of which properties of the message
              ; were evaluated by the authentication scheme being
              ; applied to yield the reported result
     method = Keyword [ [CFWS] "/" [CFWS] method-version ]
            ; a method indicates which method's result is
            ; represented by "result"; it is one of the methods
            ; explicitly defined as valid in this document
            ; or is an extension method as defined below
     method-version = 1*DIGIT [CFWS]
            ; indicates which version of the method specification is
            ; in use, corresponding to the matching entry in the IANA
            ; "Email Authentication Methods" registry; a value of "1"
            ; is assumed if this version string is absent

result = Keyword ; indicates the results of the attempt to authenticate ; the message; see below for details


     ptype = Keyword
           ; indicates whether the property being evaluated was
           ; a parameter to an SMTP command [SMTP], 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 MTA; expected to be one of the "property
           ; types" explicitly defined as valid, or an extension
           ; ptype, as defined below
     property = special-smtp-verb / Keyword
             ; indicates more specifically than "ptype" what the
             ; source of the evaluated property is; the exact meaning
             ; is specific to the method whose result is being reported
             ; and is defined more clearly below
     special-smtp-verb = "mailfrom" / "rcptto"
             ; special cases of SMTP commands [SMTP] that are made up
             ; of multiple words
     pvalue = [CFWS] ( value / [ [ local-part ] "@" ] domain-name )
            ; the value extracted from the message property defined
            ; by the "" construction

"local-part" is defined in Section 3.4.1 of [MAIL], as modified by [RFC6531].


"CFWS" is defined in Section 3.2.2 of [MAIL].


"Keyword" is defined in Section 4.1.2 of [SMTP]. It is further constrained by the necessity of being registered in the Internet Assigned Numbers Authority (IANA) registry relevant to the context in which it is used. See Sections 2.3, 2.7, and 6.

「キーワード」は、[SMTP]のセクション4.1.2で定義されています。それは、それが使用されるコンテキストに関連するInternet Assigned Numbers Authority(IANA)レジストリに登録される必要性によってさらに制約されます。セクション2.3、2.7、および6を参照してください。

The "value" is as defined in Section 5.1 of [MIME], with "quoted-string" updated as specified in [RFC6532].


The "domain-name" is as defined in Section 3.5 of [DKIM].


See Section 2.5 for a description of the authserv-id element.


If the value portion of a "pvalue" construction identifies something intended to be an email identity, then it MUST use the right-hand portion of that ABNF definition.


The list of commands eligible for use with the "smtp" ptype can be found in Section 4.1 of [SMTP].


The "propspec" may be omitted if, for example, the method was unable to extract any properties to do its evaluation yet still has a result to report. It may also be omitted if the agent generating this result wishes not to reveal such properties to downstream agents.


Where an SMTP command name is being reported as a "property", the agent generating the header field represents that command by converting it to lowercase and dropping any spaces (e.g., "MAIL FROM" becomes "mailfrom", "RCPT TO" becomes "rcptto", etc.).

SMTPコマンド名が「プロパティ」として報告されている場合、ヘッダーフィールドを生成するエージェントは、コマンドを小文字に変換してスペースを削除することでそのコマンドを表します(たとえば、「MAIL FROM」は「mailfrom」になり、「RCPT TO」は「 rcptto」など)。

A "ptype" value of "policy" indicates a policy decision about the message not specific to a property of the message that could be extracted. See Section 2.4 for details.


Examples of complete messages using this header field can be found in Appendix B.


2.3. Property Types (ptypes) and Properties
2.3. プロパティタイプ(ptypes)とプロパティ

The "ptype" in the ABNF above indicates the general type of property being described by the result being reported, upon which the reported result was based. Coupled with the "property", which is more specific, it indicates from where the reported "pvalue" was extracted. This can include a particular part of the message header or body, some part of the SMTP session, a secondary output of an authentication method (apart from its pure result), or some other aspect of the message's handling.


Combinations of ptypes and properties are registered and described in the "Email Authentication Methods" registry, coupled with the authentication methods with which they are used. This is further described in Section 6.

ptypeとプロパティの組み合わせは、「Email Authentication Methods」レジストリに登録され、それらが使用されている認証方法と組み合わせて記述されます。これについては、セクション6で詳しく説明します。

Legal values of "ptype" are as defined in the IANA "Email Authentication Property Types" registry, created by [RFC7410]. The initial values and what they typically indicate are as follows, based on [RFC7001]:

「ptype」の正当な値は、[RFC7410]によって作成されたIANA「Email Authentication Property Types」レジストリで定義されているとおりです。 [RFC7001]に基づいて、初期値とそれらが通常示すものは次のとおりです。

body: Information that was extracted from the body of the message. This might be an arbitrary string of bytes, a hash of a string of bytes, a Uniform Resource Identifier, or some other content of interest. The "property" is an indication of where within the message body the extracted content was found and can indicate an offset, identify a MIME part, etc. (At the time of this revision, no properties matching this ptype have been registered. Accordingly, this ptype may be deprecated in the future.)

body:メッセージの本文から抽出された情報。これは、任意のバイト文字列、バイト文字列のハッシュ、Uniform Resource Identifier、またはその他の関心のあるコンテンツです。 「プロパティ」は、メッセージ本文のどこに抽出されたコンテンツが見つかったかを示すものであり、オフセットを示したり、MIMEパーツを識別したりできます(このリビジョンの時点では、このptypeに一致するプロパティは登録されていません。したがって、このptypeは将来廃止される可能性があります。)

header: Indicates information that was extracted from the header of the message. This might be the value of a header field or some portion of a header field. The "property" gives a more precise indication of the place in the header from which the extraction took place.

header:メッセージのヘッダーから抽出された情報を示します。これは、ヘッダーフィールドの値またはヘッダーフィールドの一部である可能性があります。 「プロパティ」は、抽出が行われたヘッダーの場所をより正確に示します。

policy: A local policy mechanism was applied that augments or overrides the result returned by the authentication mechanism. (See Section 2.4.)

ポリシー:認証メカニズムによって返された結果を拡張またはオーバーライドするローカルポリシーメカニズムが適用されました。 (2.4項を参照してください。)

smtp: Indicates information that was extracted from an SMTP command that was used to relay the message. The "property" indicates which SMTP command included the extracted content as a parameter.

smtp:メッセージの中継に使用されたSMTPコマンドから抽出された情報を示します。 「プロパティ」は、抽出されたコンテンツをパラメーターとして含んだSMTPコマンドを示します。

Results reported using unknown ptypes MUST NOT be used in making handling decisions. They can be safely ignored by consumers.

不明なptypeを使用して報告された結果を、処理の決定に使用してはなりません(MUST NOT)。それらは消費者によって安全に無視することができます。

Entries in the "Email Authentication Methods" registry can define properties that deviate from these definitions when appropriate. Such deviations need to be clear in the registry and/or in the defining document. See Section 2.7.1 for an example.

「Email Authentication Methods」レジストリのエントリは、適切な場合にこれらの定義から逸脱するプロパティを定義できます。このような逸脱は、レジストリや定義ドキュメントで明確にする必要があります。例については、セクション2.7.1を参照してください。

2.4. The "policy" ptype
2.4. 「ポリシー」ptype

A special ptype value of "policy" is also defined. This ptype is provided to indicate that some local policy mechanism was applied that augments or even replaces (i.e., overrides) the result returned by the authentication mechanism. The property and value in this case identify the local policy that was applied and the result it returned.


For example, a DKIM signature is not required to include the Subject header field in the set of fields that are signed. An ADMD receiving such a message might decide that such a signature is unacceptable, even if it passes, because the content of the Subject header field could be altered post-signing without invalidating the signature. Such an ADMD could replace the DKIM "pass" result with a "policy" result and then also include the following in the corresponding Authentication-Results field:


... dkim=policy policy.dkim-rules=unsigned-subject ...

... dkim = policy policy.dkim-rules = unsigned-subject ...

In this case, the property is "dkim-rules", indicating that some local check by that name took place and that check returned a result of "unsigned-subject". These are arbitrary names selected by (and presumably used within) the ADMD making use of them, so they are not normally registered with IANA or otherwise specified apart from setting syntax restrictions that allow for easy parsing within the rest of the header field.


This ptype existed in the original specification for this header field [RFC5451], but without a complete description or example of intended use. As a result, it has not seen any practical use to date that matches its intended purpose. These added details are provided to guide implementers toward proper use.


2.5. Authentication Service Identifier Field
2.5. 認証サービス識別子フィールド

Every Authentication-Results header field has an authentication service identifier field (authserv-id above). Specifically, this is any string intended to identify the authentication service within the ADMD that conducted authentication checks on the message. This identifier is intended to be machine-readable and not necessarily meaningful to users.


Note that in an EAI-formatted message, this identifier may be expressed in UTF-8.


Since agents consuming this field will use this identifier to determine whether its contents are of interest (and are safe to use), the uniqueness of the identifier MUST be guaranteed by the ADMD that generates it and MUST pertain to that ADMD. MUAs or downstream filters SHOULD use this identifier to determine whether or not the data contained in an Authentication-Results header field ought to be used or ignored.

このフィールドを使用するエージェントはこの識別子を使用して、その内容が重要である(そして安全に使用できる)かどうかを判断するため、識別子の一意性は、それを生成するADMDによって保証されなければならず(MUST)、そのADMDに関係する必要があります。 MUAまたはダウンストリームフィルターは、この識別子を使用して、Authentication-Resultsヘッダーフィールドに含まれるデータを使用または無視する必要があるかどうかを判断する必要があります(SHOULD)。

For simplicity and scalability, the authentication service identifier SHOULD be a common token used throughout the ADMD. Common practice is to use the DNS domain name used by or within that ADMD, sometimes called the "organizational domain", but this is not strictly necessary.


For tracing and debugging purposes, the authentication service identifier can instead be the specific hostname of the MTA performing the authentication check whose result is being reported. Moreover, some implementations define a substructure to the identifier; such structures are outside of the scope of this specification.


Note, however, that using a local, relative identifier like a flat hostname, rather than a hierarchical and globally unique ADMD identifier like a DNS domain name, makes configuration more difficult for large sites. The hierarchical identifier permits aggregating related, trusted systems together under a single, parent identifier, which in turn permits assessing the trust relationship with a single reference. The alternative is a flat namespace requiring individually listing each trusted system. Since consumers will use the identifier to determine whether to use the contents of the header field:


o Changes to the identifier impose a large, centralized administrative burden.

o 識別子を変更すると、大きな集中管理上の負担がかかります。

o Ongoing administrative changes require constantly updating this centralized table, making it difficult to ensure that an MUA or downstream filter will have access to accurate information for assessing the usability of the header field's content. In particular, consumers of the header field will need to know not only the current identifier(s) in use but previous ones as well to account for delivery latency or later reassessment of the header field's content.

o 進行中の管理上の変更では、この集中テーブルを常に更新する必要があるため、MUAまたはダウンストリームフィルターがヘッダーフィールドのコンテンツの有用性を評価するための正確な情報にアクセスできるようにすることは困難です。特に、ヘッダーフィールドのコンシューマーは、現在の識別子だけでなく以前の識別子も知っている必要があり、配信の遅延やヘッダーフィールドのコンテンツの再評価を考慮する必要があります。

Examples of valid authentication service identifiers are "", "", "", and "example-auth".


2.6. Version Tokens
2.6. バージョントークン

The grammar above provides for the optional inclusion of versions on both the header field itself (attached to the authserv-id token) and on each of the methods being reported. The method version refers to the method itself, which is specified in the documents describing those methods, while the authserv-id version refers to this document and thus the syntax of this header field.


The purpose of including these is to avoid misinterpretation of the results. That is, if a parser finds a version after an authserv-id that it does not explicitly know, it can immediately discontinue trying to parse, since what follows might not be in an expected format. For a method version, the parser SHOULD ignore a method result if the version is not supported in case the semantics of the result have a different meaning than what is expected. For example, if a hypothetical DKIM version 2 yielded a "pass" result for different reasons than version 1 does, a consumer of this field might not want to use the altered semantics. Allowing versions in the syntax is a way to indicate this and let the consumer of the header field decide.


2.7. Defined Methods and Result Values
2.7. 定義されたメソッドと結果値

Each individual authentication method returns one of a set of specific result values. The subsections below provide references to the documents defining the authentication methods specifically supported by this document, and their corresponding result values. Verifiers SHOULD use these values as described below. New methods not specified in this document, but intended to be supported by the header field defined here, MUST include a similar result table either in their defining documents or in supplementary ones.


2.7.1. DKIM
2.7.1. DKIM

DKIM is represented by the "dkim" method and is defined in [DKIM].


A signature is "acceptable to the ADMD" if it passes local policy checks (or there are no specific local policy checks). For example, an ADMD policy might require that the signature(s) on the message be added using the DNS domain present in the From header field of the message, thus making third-party signatures unacceptable even if they verify.


The DKIM result set is as follows:


none: The message was not signed.


pass: The message was signed, the signature or signatures were acceptable to the ADMD, and the signature(s) passed verification tests.


fail: The message was signed and the signature or signatures were acceptable to the ADMD, but they failed the verification test(s).


policy: The message was signed, but some aspect of the signature or signatures was not acceptable to the ADMD.


neutral: The message was signed, but the signature or signatures contained syntax errors or were not otherwise able to be processed. This result is also used for other failures not covered elsewhere in this list.


temperror: The message could not be verified due to some error that is likely transient in nature, such as a temporary inability to retrieve a public key. A later attempt may produce a final result.


permerror: The message could not be verified due to some error that is unrecoverable, such as a required header field being absent. A later attempt is unlikely to produce a final result.


DKIM results are reported using a ptype of "header". The property, however, represents one of the tags found in the DKIM-Signature header field rather than a distinct header field. For example, the ptype-property combination "header.d" refers to the content of the "d" (signing domain) tag from within the signature header field, and not a distinct header field called "d".


Note that in an EAI-formatted message, the values of the "d" and "i" properties can be expressed in UTF-8.


In addition to previous registrations, this document registers the DKIM tags "a" (cryptographic algorithm used to sign the message) and "s" (selector) as reportable properties. These can be used to aid receivers during post-verification processing. In particular, [RFC8301] obsoleted use of the "rsa-sha1" algorithm in DKIM, so it is important to be able to distinguish such signatures from those using preferred algorithms.

以前の登録に加えて、このドキュメントでは、DKIMタグ "a"(メッセージの署名に使用される暗号化アルゴリズム)および "s"(セレクター)をレポート可能なプロパティとして登録します。これらは、検証後の処理中に受信者を支援するために使用できます。特に、[RFC8301]はDKIMの「rsa-sha1」アルゴリズムの使用を廃止したため、このような署名を、好ましいアルゴリズムを使用したものと区別できるようにすることが重要です。

The ability to report different DKIM results for a message with multiple signatures is described in [RFC6008].


[DKIM] advises that if a message fails verification, it is to be treated as an unsigned message. A report of "fail" here permits the receiver of the report to decide how to handle the failure. A report of "neutral" or "none" preempts that choice, ensuring that the message will be treated as if it had not been signed.

[DKIM]は、メッセージが検証に失敗した場合、署名されていないメッセージとして扱われることを勧めています。ここでの「失敗」のレポートにより、レポートの受信者は失敗の処理方法を決定できます。 「中立」または「なし」のレポートはその選択よりも優先され、メッセージが署名されていないかのように扱われることを保証します。

2.7.2. SPF
2.7.2. SPF

SPF uses the "spf" method name. The result values for SPF are defined in Section 2.6 of [SPF], and those definitions are included here by reference:

SPFは「spf」メソッド名を使用します。 SPFの結果値は[SPF]のセクション2.6で定義されており、それらの定義は参照によりここに含まれています。

      |    Code   | Meaning                      |
      | none      | [SPF], Section 2.6.1         |
      | pass      | [SPF], Section 2.6.3         |
      | fail      | [SPF], Section 2.6.4         |
      | softfail  | [SPF], Section 2.6.5         |
      | policy    | RFC 8601, Section 2.4        |
      | neutral   | [SPF], Section 2.6.2         |
      | temperror | [SPF], Section 2.6.6         |
      | permerror | [SPF], Section 2.6.7         |

These result codes are used in the context of this specification to reflect the result returned by the component conducting SPF evaluation.


For SPF, the ptype used is "smtp", and the property is either "mailfrom" or "helo", since those values are the ones SPF can evaluate. (If the SMTP client issued the EHLO command instead of HELO, the property used is "helo".)

SPFの場合、使用されるptypeは「smtp」で、プロパティは「mailfrom」または「helo」です。これらの値はSPFが評価できる値であるためです。 (SMTPクライアントがHELOではなくEHLOコマンドを発行した場合、使用されるプロパティは "helo"です。)

Note that in an EAI-formatted message, the local-part of the "mailfrom" can be expressed in UTF-8 and the domain part can be expressed as a U-label.


For this method, an additional result of "policy" is defined, which means the client was authorized to inject or relay mail on behalf of the sender's DNS domain according to the authentication method's algorithm, but local policy dictates that the result is unacceptable. For example, "policy" might be used if SPF returns a "pass" result, but a local policy check matches the sending DNS domain to one found in an explicit list of unacceptable DNS domains (e.g., spammers).


If the retrieved sender policies used to evaluate SPF do not contain explicit provisions for authenticating the local-part (see Section 3.4.1 of [MAIL]) of an address, the "pvalue" reported along with results for this mechanism SHOULD NOT include the local-part or the following "@" character.

SPFの評価に使用される取得された送信者ポリシーに、アドレスのローカル部分([MAIL]のセクション3.4.1を参照)を認証する明示的な規定が含まれていない場合、このメカニズムの結果とともに報告される「pvalue」には、 local-partまたはそれに続く「@」文字。

2.7.3. "iprev"
2.7.3. 「iprev」

The result values used by the "iprev" method, defined in Section 3, are as follows:


pass: The DNS evaluation succeeded, i.e., the "reverse" and "forward" lookup results were returned and were in agreement.


fail: The DNS evaluation failed. In particular, the "reverse" and "forward" lookups each produced results, but they were not in agreement, or the "forward" query completed but produced no result, e.g., a DNS RCODE of 3, commonly known as NXDOMAIN, or an RCODE of 0 (NOERROR) in a reply containing no answers, was returned.

fail:DNS評価は失敗しました。特に、「リバース」および「フォワード」ルックアップはそれぞれ結果を生成しましたが、一致しませんでした、または「フォワード」クエリは完了しましたが、結果を生成しませんでした。たとえば、DNS RCODE 3、通称NXDOMAIN、または回答を含まない返信でRCODEの0(NOERROR)が返されました。

temperror: The DNS evaluation could not be completed due to some error that is likely transient in nature, such as a temporary DNS error, e.g., a DNS RCODE of 2, commonly known as SERVFAIL, or other error condition resulted. A later attempt may produce a final result.

temperror:一時的なDNSエラー(例:DNS RCODE 2、一般的にSERVFAILと呼ばれる)など、本質的に一時的なエラーが原因でDNS評価を完了できなかったか、その他のエラー状態が発生しました。後で試行すると、最終結果が生成される場合があります。

permerror: The DNS evaluation could not be completed because no PTR data are published for the connecting IP address, e.g., a DNS RCODE of 3, commonly known as NXDOMAIN, or an RCODE of 0 (NOERROR) in a reply containing no answers, was returned. This prevented completion of the evaluation. A later attempt is unlikely to produce a final result.

permerror:接続しているIPアドレスのPTRデータが公開されていないため、DNS評価を完了できませんでした。たとえば、DNS RCODE 3(一般にNXDOMAINとして知られている)、またはRCODE 0(NOERROR)は、応答を含まない応答では、戻ってきた。これは評価の完了を妨げた。後で試行しても、最終的な結果は得られません。

There is no "none" for this method, since any TCP connection delivering email has an IP address associated with it, so some kind of evaluation will always be possible.


The result is reported using a ptype of "policy" (as this is not part of any established protocol) and a property of "iprev".


For discussion of the format of DNS replies, see "Domain names - implementation and specification" [DNS].


2.7.4. SMTP AUTH
2.7.4. SMTP AUTH

SMTP AUTH (defined in [AUTH]) is represented by the "auth" method. Its result values are as follows:

SMTP AUTH([AUTH]で定義)は、「auth」メソッドで表されます。結果の値は次のとおりです。

none: SMTP authentication was not attempted.


pass: The SMTP client authenticated to the server reporting the result using the protocol described in [AUTH].


fail: The SMTP client attempted to authenticate to the server using the protocol described in [AUTH] but was not successful (such as providing a valid identity but an incorrect password).


temperror: The SMTP client attempted to authenticate using the protocol described in [AUTH] but was not able to complete the attempt due to some error that is likely transient in nature, such as a temporary directory service lookup error. A later attempt may produce a final result.


permerror: The SMTP client attempted to authenticate using the protocol described in [AUTH] but was not able to complete the attempt due to some error that is likely not transient in nature, such as a permanent directory service lookup error. A later attempt is not likely to produce a final result.


The result of AUTH is reported using a ptype of "smtp" and a property of either:


o "auth", in which case the value is the authorization identity generated by the exchange initiated by the AUTH command; or

o 「auth」。この場合、値は、AUTHコマンドによって開始された交換によって生成された許可IDです。または

o "mailfrom", in which case the value is the mailbox identified by the AUTH parameter used with the MAIL FROM command.

o 「mailfrom」。この場合、値はMAIL FROMコマンドで使用されるAUTHパラメータによって識別されるメールボックスです。

Note that in an EAI-formatted message, the local-part can be expressed in UTF-8 and the domain can be expressed as a U-label.


If both identities are available, both can be reported. For example, consider this command issued by a client that has completed session authentication with the AUTH command resulting in an authorized identity of "client@c.example":


     MAIL FROM:<alice@a.example> AUTH=<bob@b.example>

This could result in a "resinfo" construction like so:


     ; auth=pass smtp.auth=client@c.example smtp.mailfrom=bob@b.example

Note that in all cases other than "pass", the message was sent by an unauthenticated client. All non-"pass" cases SHOULD thus be treated as equivalent with respect to this method.


2.7.5. Other Registered Codes
2.7.5. その他の登録済みコード

Result codes were also registered in other RFCs as follows:


o Vouch By Reference (in [AR-VBR], represented by "vbr").

o 参照による保証([AR-VBR]では、「vbr」で表されます)。

o Authorized Third-Party Signatures (in [ATPS], represented by "dkim-atps").

o 承認されたサードパーティの署名([ATPS]内、「dkim-atps」で表されます)。

o Author Domain Signing Practices (in [ADSP], represented by "dkim-adsp").

o 作成者ドメイン署名の実践([ADSP]内、「dkim-adsp」で表される)。

o Require-Recipient-Valid-Since (in [RRVS], represented by "rrvs").

o Require-Recipient-Valid-Since([RRVS]では、「rrvs」で表されます)。

o S/MIME (in [SMIME-REG], represented by "smime").

o S / MIME([SMIME-REG]内、「smime」で表されます)。

Note that in an EAI-formatted message, "" and "", which are already registered, can be expressed as U-labels.


2.7.6. Extension Methods
2.7.6. 拡張メソッド

Additional authentication method identifiers (extension methods) may be defined in the future by later revisions or extensions to this specification. These method identifiers are registered with IANA and, preferably, published in an RFC. See Section 6 for further details.


Extension methods can be defined for the following reasons:


1. To allow additional information from new authentication systems to be communicated to MUAs or downstream filters. The names of such identifiers ought to reflect the name of the method being defined but ought not be needlessly long.

1. 新しい認証システムからの追加情報をMUAまたはダウンストリームフィルターに伝達できるようにするため。そのような識別子の名前は、定義されているメソッドの名前を反映するべきですが、不必要に長くあるべきではありません。

2. To allow the creation of "sub-identifiers" that indicate different levels of authentication and differentiate between their relative strengths, e.g., "auth1-weak" and "auth1-strong".

2. 異なる認証レベルを示し、それらの相対的な強さを区別する「サブ識別子」の作成を許可するため。たとえば、「auth1-weak」と「auth1-strong」。

Authentication method implementers are encouraged to provide adequate information, via message header field comments if necessary, to allow an MUA developer to understand or relay ancillary details of authentication results. For example, if it might be of interest to relay what data were used to perform an evaluation, such information could be relayed as a comment in the header field, such as:


                  foo=pass bar.baz=blob (2 of 3 tests OK)

Experimental method identifiers MUST only be used within ADMDs that have explicitly consented to use them. These method identifiers and the parameters associated with them are not documented formally. Therefore, they are subject to change at any time and not suitable for production use. Any MTA, MUA, or downstream filter intended for production use SHOULD ignore or delete any Authentication-Results header field that includes an experimental (unknown) method identifier.


2.7.7. Extension Result Codes
2.7.7. 拡張結果コード

Additional result codes (extension results) might be defined in the future by later revisions or extensions to this specification. Non-experimental result codes MUST be registered with IANA (and, preferably, published in an RFC). See Section 6 for further details.


Experimental results MUST only be used within ADMDs that have explicitly consented to use them. These results and the parameters associated with them are not formally documented. Therefore, they are subject to change at any time and not suitable for production use. Any MTA, MUA, or downstream filter intended for production use SHOULD ignore or delete any Authentication-Results header field that includes an extension result.


3. The "iprev" Authentication Method
3. 「iprev」認証方式

This section defines an additional authentication method called "iprev".


"iprev" is an attempt to verify that a client appears to be valid based on some DNS queries, which is to say that the IP address is explicitly associated with a domain name. Upon receiving a session initiation of some kind from a client, the IP address of the client peer is queried for matching names (i.e., a number-to-name translation, also known as a "reverse lookup" or a "PTR" record query). Once that result is acquired, a lookup of each of the names (i.e., a name-to-number translation, or an "A" or "AAAA" record query) thus retrieved is done. The response to this second check will typically result in at least one mapping back to the client's IP address.


Expressed as an algorithm: If the client peer's IP address is I, the list of names to which I maps (after a "PTR" query) is the set N, and the union of IP addresses to which each member of N maps (after corresponding "A" and "AAAA" queries) is L, then this test is successful if I is an element of L.


Often an MTA receiving a connection that fails this test will simply reject the connection using the enhanced status code defined in [AUTH-ESC]. If an operator instead wishes to make this information available to downstream agents as a factor in handling decisions, it records a result in accordance with Section 2.7.3.


The response to a "PTR" query could contain multiple names. To prevent heavy DNS loads, agents performing these queries MUST be implemented such that the number of names evaluated by generation of corresponding "A" or "AAAA" queries is limited so as not to be unduly taxing to the DNS infrastructure, though it MAY be configurable by an administrator. As an example, Section 4.6.4 of [SPF] chose a limit of 10 for its implementation of this algorithm.


"DNS Extensions to Support IP Version 6" [DNS-IP6] discusses the query formats for the IPv6 case.


There is some contention regarding the wisdom and reliability of this test. For example, in some regions, it can be difficult for this test ever to pass because the practice of arranging to match the forward and reverse DNS is infrequently observed. Therefore, the precise implementation details of how a verifier performs an "iprev" test are not specified here. The verifier MAY report a successful or failed "iprev" test at its discretion having done some kind of check of the validity of the connection's identity using DNS. It is incumbent upon an agent making use of the reported "iprev" result to understand what exactly that particular verifier is attempting to report.


Extensive discussion of reverse DNS mapping and its implications can be found in "Considerations for the use of DNS Reverse Mapping" [DNSOP-REVERSE]. In particular, it recommends that applications avoid using this test as a means of authentication or security. Its presence in this document is not an endorsement but is merely acknowledgment that the method remains common and provides the means to relay the results of that test.


4. Adding the Header Field to a Message
4. メッセージへのヘッダーフィールドの追加

This specification makes no attempt to evaluate the relative strengths of various message authentication methods that may become available. The methods listed are an order-independent set; their sequence does not indicate relative strength or importance of one method over another. Instead, the MUA or downstream filter consuming this header field is to interpret the result of each method based on its own knowledge of what that method evaluates.


Each "method" MUST refer to an authentication method declared in the IANA registry or an extension method as described in Section 2.7.6, and each "result" MUST refer to a result code declared in the IANA registry or an extension result code as defined in Section 2.7.7. See Section 6 for further information about the registered methods and result codes.


An MTA compliant with this specification adds this header field (after performing one or more message authentication tests) to indicate which MTA or ADMD performed the test, which test was applied, and what the result was. If an MTA applies more than one such test, it adds this header field either once per test or once indicating all of the results. An MTA MUST NOT add a result to an existing header field.

この仕様に準拠するMTAは、このヘッダーフィールドを追加して(1つ以上のメッセージ認証テストを実行した後)、どのMTAまたはADMDがテストを実行し、どのテストを適用し、結果を示しました。 MTAがそのようなテストを複数適用する場合は、テストごとに1回、またはすべての結果を示すために、このヘッダーフィールドを追加します。 MTAは、既存のヘッダーフィールドに結果を追加してはなりません(MUST NOT)。

An MTA MAY add this header field containing only the authentication service identifier portion and the "none" token (see Section 2.2) to indicate explicitly that no message authentication schemes were applied prior to delivery of this message.


An MTA adding this header field has to take steps to identify it as legitimate to the MUAs or downstream filters that will ultimately consume its content. One process to do so is described in Section 5. Further measures may be necessary in some environments. Some possible solutions are enumerated in Section 7.1. This document does not mandate any specific solution to this issue, as each environment has its own facilities and limitations.


Most known message authentication methods focus on a particular identifier to evaluate. SPF differs in that it can yield a result based on more than one identifier; specifically, SPF can evaluate the RFC5321.HELO parameter or the RFC5321.MailFrom parameter. When generating this field to report those results, only the parameter that yielded the result is included.

ほとんどの既知のメッセージ認証方法は、評価する特定の識別子に焦点を当てています。 SPFは、複数の識別子に基づいて結果を生成できるという点で異なります。具体的には、SPFはRFC5321.HELOパラメーターまたはRFC5321.MailFromパラメーターを評価できます。これらの結果を報告するためにこのフィールドを生成する場合、結果を生成したパラメーターのみが含まれます。

For MTAs that add this header field, adding header fields in order (at the top), per Section 3.6 of [MAIL], is particularly important. Moreover, this header field SHOULD be inserted above any other trace header fields such MTAs might prepend. This placement allows easy detection of header fields that can be trusted.


End users making direct use of this header field might inadvertently trust information that has not been properly vetted. If, for example, a basic SPF result were to be relayed that claims an authenticated addr-spec, the local-part of that addr-spec has actually not been authenticated. Thus, an MTA adding this header field SHOULD NOT include any data that have not been authenticated by the method(s) being applied. Moreover, MUAs SHOULD NOT render to users such information if it is presented by a method known not to authenticate it.

このヘッダーフィールドを直接使用するエンドユーザーは、適切に検査されていない情報を誤って信頼する可能性があります。たとえば、認証されたaddr-specを要求する基本的なSPF結果が中継される場合、そのaddr-specのローカル部分は実際には認証されていません。したがって、このヘッダーフィールドを追加するMTAには、適用されているメソッドによって認証されていないデータを含めるべきではありません(SHOULD NOT)。さらに、それを認証しないことがわかっている方法で提示された場合、MUAはそのような情報をユーザーに表示しないでください。

4.1. Header Field Position and Interpretation
4.1. ヘッダーフィールドの位置と解釈

In order to ensure non-ambiguous results and avoid the impact of false header fields, MUAs and downstream filters SHOULD NOT interpret this header field unless specifically configured to do so by the user or administrator. That is, this interpretation should not be "on by default". Naturally then, users or administrators ought not activate such a feature unless (1) they are certain the header field will be validly added by an agent within the ADMD that accepts the mail that is ultimately read by the MUA, and (2) instances of the header field that appear to originate within the ADMD but are actually added by foreign MTAs will be removed before delivery.

明確な結果を保証し、誤ったヘッダーフィールドの影響を回避するために、MUAとダウンストリームフィルターは、ユーザーまたは管理者によって特別に構成されていない限り、このヘッダーフィールドを解釈しないでください。つまり、この解釈は「デフォルトでオン」であってはなりません。当然、ユーザーまたは管理者は、(1)最終的にMUAによって読み取られるメールを受け入れるADMD内のエージェントによってヘッダーフィールドが有効に追加されることが確実である場合、および(2)のインスタンスでない限り、このような機能をアクティブにすべきではありません。 ADMD内で発生したように見えても、実際には外部MTAによって追加されたヘッダーフィールドは、配信前に削除されます。

Furthermore, MUAs and downstream filters SHOULD NOT interpret this header field unless the authentication service identifier of the header field is used within the ADMD as configured by the user or administrator.


MUAs and downstream filters MUST ignore any result reported using a "result" not specified in the IANA "Result Code" registry or a "ptype" not listed in the "Email Authentication Property Types" registry for such values as defined in Section 6. Moreover, such agents MUST ignore a result indicated for any "method" they do not specifically support. The exception to this is experimental methods as discussed in Section 2.7.6.

MUAとダウンストリームフィルターは、IANAの「結果コード」レジストリで指定されていない「結果」またはセクション6で定義されているような値の「メール認証プロパティタイプ」レジストリにリストされていない「ptype」を使用して報告された結果を無視する必要があります。 、そのようなエージェントは、具体的にサポートしていない「メソッド」に対して示された結果を無視する必要があります。これに対する例外は、セクション2.7.6で説明する実験的方法です。

An MUA SHOULD NOT reveal these results to end users, absent careful "human factors" design considerations and testing, for the presentation of trust-related materials. For example, an attacker could register (note the digit "1" (one)) and send signed mail to intended victims; a verifier would detect that the signature was valid and report a "pass" even though it's clear the DNS domain name was intended to mislead. See Section 7.2 for further discussion.

MUAは、信頼に関連する資料を提示するための注意深い「ヒューマンファクター」の設計上の考慮事項とテストがない限り、これらの結果をエンドユーザーに明らかにすべきではありません。たとえば、攻撃者は、examp1e.comを登録し(数字の "1"(1)に注意)、意図した被害者に署名付きメールを送信する可能性があります。 DNSドメイン名が誤解を招くように意図されていたことが明らかであっても、検証者は署名が有効であることを検出し、「合格」を報告します。詳細については、セクション7.2を参照してください。

As stated in Section 2.1, this header field MUST be treated as though it were a trace header field as defined in Section 3.6.7 of [MAIL] and hence MUST NOT be reordered and MUST be prepended to the message, so that there is generally some indication upon delivery of where in the chain of handling MTAs the message authentication was done.

セクション2.1で述べたように、このヘッダーフィールドは、[MAIL]のセクション3.6.7で定義されているように、トレースヘッダーフィールドであるかのように処理する必要があるため、並べ替えてはならず、メッセージの先頭に付加する必要があります。 MTAを処理するチェーンのどこに配信されたかを示すメッセージ認証が行われました。

Note that there are a few message handlers that are only capable of appending new header fields to a message. Strictly speaking, these handlers are not compliant with this specification. They can still add the header field to carry authentication details, but any signal about where in the handling chain the work was done may be lost. Consumers SHOULD be designed such that this can be tolerated, especially from a producer known to have this limitation.


MUAs SHOULD ignore instances of this header field discovered within message/rfc822 MIME attachments. They are likely to contain the results of authentication checks done in the past, possibly long ago, and have no contemporary value. Due caution therefore needs to be taken when choosing to consume them.

MUAは、message / rfc822 MIME添付ファイル内で発見されたこのヘッダーフィールドのインスタンスを無視する必要があります(SHOULD)。それらはおそらく過去に、おそらくずっと前に行われた認証チェックの結果を含んでいる可能性が高く、現代的な価値はありません。したがって、それらを消費することを選択する際には十分な注意が必要です。

Further discussion of these topics can be found in Section 7 below.


4.2. Local Policy Enforcement
4.2. ローカルポリシーの施行

Some sites have a local policy that considers any particular authentication policy's non-recoverable failure results (typically "fail" or similar) as justification for rejecting the message. In such cases, the border MTA SHOULD issue an SMTP rejection response to the message, rather than adding this header field and allowing the message to proceed toward delivery. This is more desirable than allowing the message to reach an internal host's MTA or spam filter, thus possibly generating a local rejection such as a Delivery Status Notification (DSN) [DSN] to a forged originator. Such generated rejections are colloquially known as "backscatter".


The same MAY also be done for local policy decisions overriding the results of the authentication methods (e.g., the "policy" result codes described in Section 2.7).


Such rejections at the SMTP protocol level are not possible if local policy is enforced at the MUA and not the MTA.


5. Removing Existing Header Fields
5. 既存のヘッダーフィールドの削除

To mitigate the impact of forged header fields, any MTA conforming to this specification MUST delete any discovered instance of this header field that claims, by virtue of its authentication service identifier, to have been added within its trust boundary but that did not come directly from another trusted MTA. For example, an MTA for receiving a message MUST delete or otherwise obscure any instance of this header field bearing an authentication service identifier indicating that the header field was added within prior to adding its own header fields. This could mean each internal MTA will need to be configured with a list of other known, trusted MTAs that are thus expected to be using that same identifier.


In the case of EAI-formatted messages, this test is done after converting A-labels into U-labels.


For simplicity and maximum security, a border MTA could remove all instances of this header field on mail crossing into its trust boundary. However, this may conflict with the desire to access authentication results performed by trusted external service providers. It may also invalidate signed messages whose signatures cover external instances of this header field. A more robust border MTA could allow a specific list of authenticating MTAs whose information is to be admitted, removing the header field originating from all others.


As stated in Section 1.2, a formal definition of "trust boundary" is deliberately not made here. It is entirely possible that a border MTA for will explicitly trust authentication results asserted by upstream host even though they exist in completely disjoint administrative boundaries. In that case, the border MTA MAY elect not to delete those results; moreover, the upstream host doing some authentication work could apply a signing technology such as [DKIM] on its own results to assure downstream hosts of their authenticity. An example of this is provided in Appendix B.

セクション1.2で述べたように、ここでは「信頼境界」の正式な定義は意図的に行われていません。 example.comの境界MTAが、上流のホストexample.netによってアサートされた認証結果を、完全にばらばらの管理境界に存在していても、明示的に信頼することは完全に可能です。その場合、境界MTAはそれらの結果を削除しないことを選択する場合があります。さらに、何らかの認証作業を行う上流ホストは、[DKIM]などの署名技術を独自の結果に適用して、下流ホストの認証を保証することができます。この例を付録Bに示します。

Similarly, in the case of messages signed using [DKIM] or other message-signing methods that sign header fields, this removal action could invalidate one or more signatures on the message if they covered the header field to be removed. This behavior can be desirable, since there's little value in validating the signature on a message with forged header fields. However, signing agents MAY therefore elect to omit these header fields from signing to avoid this situation.


An MTA SHOULD remove any instance of this header field bearing a version (express or implied) that it does not support. However, an MTA MUST remove such a header field if the SMTP connection [SMTP] relaying the message is not from a trusted internal MTA. (As discussed above, this too can result in invalidation of signatures.) This means the MTA needs to be able to understand versions of this header field at least as late as the ones understood by the MUAs or other consumers within its ADMD.

MTAは、サポートされていないバージョン(明示または暗示)を含むこのヘッダーフィールドのインスタンスを削除する必要があります(SHOULD)。ただし、メッセージをリレーするSMTP接続[SMTP]が信頼できる内部MTAからのものでない場合、MTAはこのようなヘッダーフィールドを削除する必要があります。 (上で説明したように、これも署名の無効化につながる可能性があります。)つまり、MTAは、このヘッダーフィールドのバージョンを、少なくともADUA内のMUAまたは他のコンシューマーが理解するバージョンと同じくらい遅く理解できる必要があります。

6. IANA Considerations
6. IANAに関する考慮事項

IANA has registered the defined header field and created registries as described below. These registry actions were originally defined by [RFC5451] and updated by [RFC6577] and [RFC7001]. The created registries were further updated in [RFC7601] to make them more complete.


Each registry has two related sections below. The first describes the registry and its update procedures, which are unchanged from [RFC7601]. The second enumerates changes to entries that are relevant to this document.

各レジストリには、以下の2つの関連セクションがあります。 1つ目は、レジストリとその更新手順について説明しており、[RFC7601]から変更されていません。 2番目は、このドキュメントに関連するエントリへの変更を列挙します。

6.1. The Authentication-Results Header Field
6.1. Authentication-Resultsヘッダーフィールド

The Authentication-Results header field was added to the IANA "Permanent Message Header Field Names" registry, per the procedure found in [IANA-HEADERS]. That entry has been updated to reference this document. The following is the registration template:

[IANA-HEADERS]にある手順に従って、Authentication-ResultsヘッダーフィールドがIANAの「Permanent Message Header Field Names」レジストリに追加されました。そのエントリは、このドキュメントを参照するように更新されました。以下は登録テンプレートです。

      Header field name: Authentication-Results
      Applicable protocol: mail [MAIL]
      Status: standard
      Author/Change controller: IETF
      Specification document(s): RFC 8601
      Related information: none
6.2. "Email Authentication Methods" Registry Description
6.2. 「電子メール認証方法」レジストリの説明

Names of message authentication methods supported by this specification have been registered with IANA, with the exception of experimental names as described in Section 2.7.6. Along with each method are recorded the properties that accompany the method's result.


The "Email Authentication Parameters" group, and within it the "Email Authentication Methods" registry, were created by [RFC5451] for this purpose. [RFC6577] added a "Status" field for each entry. [RFC7001] amended the rules governing that registry and also added a "Version" field to the registry.

「Email Authentication Parameters」グループ、およびその中の「Email Authentication Methods」レジストリは、この目的のために[RFC5451]によって作成されました。 [RFC6577]は、各エントリに「ステータス」フィールドを追加しました。 [RFC7001]は、そのレジストリを管理するルールを修正し、「バージョン」フィールドをレジストリに追加しました。

The reference for that registry has been updated to reference this document.


New entries are assigned only for values that have received Expert Review, per [IANA-CONSIDERATIONS]. The designated expert shall be appointed by the IESG. The designated expert has discretion to request that a publication be referenced if a clear, concise definition of the authentication method cannot be provided, such that interoperability is assured. Registrations should otherwise be permitted. The designated expert can also handle requests to mark any current registration as "deprecated".


No two entries can have the same combination of method, ptype, and property.


An entry in this registry contains the following:


Method: the name of the method.


Definition: a reference to the document that created this entry, if any (see below).


ptype: a "ptype" value appropriate for use with that method.


Property: a "property" value matching that "ptype" also appropriate for use with that method.


Value: a brief description of the value to be supplied with that method/ptype/property tuple.

値:そのメソッド/ ptype /プロパティタプルで提供される値の簡単な説明。

Status: the status of this entry, which is one of the following:


active: The entry is in current use.


deprecated: The entry is no longer in current use.


Version: a version number associated with the method (preferably starting at "1").


The "Definition" field will typically refer to a permanent document, or at least some descriptive text, where additional information about the entry being added can be found. This might in turn reference the document where the method is defined so that all of the semantics around creating or interpreting an Authentication-Results header field using this method, ptype, and property can be understood.


6.3. "Email Authentication Methods" Registry Update
6.3. 「メール認証方法」レジストリの更新

The following entries in this registry have been updated to replace [RFC7601] with this document:


     |   Method   | ptype  | Property                         |
     |    auth    |  smtp  | auth                             |
     |    auth    |  smtp  | mailfrom                         |
     |    dkim    | header | d                                |
     |    dkim    | header | i                                |
     |   iprev    | policy | iprev                            |
     |    spf     |  smtp  | mailfrom                         |
     |    spf     |  smtp  | helo                             |

Notably, the DomainKeys and Sender ID entries are not updated to refer to this revised specification, as they are considered obsolete. Accordingly, IANA has changed the "Status" field of the "sender-id" entry in this table to "deprecated".

特に、DomainKeysとSender IDのエントリは、廃止されたと見なされているため、この改訂された仕様を参照するように更新されていません。したがって、IANAはこの表の「sender-id」エントリの「Status」フィールドを「deprecated」に変更しました。

Finally, two new entries have been added to this registry, as follows:


6.3.1. "header.a" for DKIM
6.3.1. DKIMの場合は「header.a」

Method: dkim


Definition: RFC 8601

定義:RFC 8601

ptype: header


Property: a


Value: value of signature "a" tag


Status: active


Version: 1


6.3.2. "header.s" for DKIM
6.3.2. DKIMの場合は「header.s」

Method: dkim


Definition: RFC 8601

定義:RFC 8601

ptype: header


Property: s


Value: value of signature "s" tag


Status: active


Version: 1


6.4. "Email Authentication Property Types" Registry Description
6.4. 「電子メール認証プロパティタイプ」レジストリの説明

[RFC7410] created the "Email Authentication Property Types" registry.

[RFC7410]は、「Email Authentication Property Types」レジストリを作成しました。

Entries in this registry are subject to the Expert Review rules as described in [IANA-CONSIDERATIONS]. Each entry in the registry requires the following values:


ptype: the name of the ptype being registered, which must fit within the ABNF described in Section 2.2.


Definition: an optional reference to a defining specification.


Description: a brief description of what sort of information this "ptype" is meant to cover.


For new entries, the designated expert needs to ensure that the description provided for the new entry adequately describes the intended use. An example would be helpful to include in the entry's defining document (if any), although entries in the "Email Authentication Methods" registry or the "Email Authentication Result Names" registry might also serve as examples of intended use.

新しいエントリの場合、指定された専門家は、新しいエントリに提供された説明が使用目的を適切に説明していることを確認する必要があります。 「メール認証方式」レジストリーまたは「メール認証結果名」レジストリーのエントリーも意図された使用例として役立つ場合がありますが、エントリーを定義する文書(ある場合)に含めると例が役立ちます。

As this is a complete restatement of the definition and rules for this registry, IANA has updated this registry to show Section 2.3 of this document as the current definitions for the "body", "header", "policy", and "smtp" entries of that registry.


6.5. "Email Authentication Property Types" Registry Update
6.5. 「電子メール認証プロパティタイプ」レジストリの更新

All current entries in this registry have been updated to replace [RFC7601] with this document.


6.6. "Email Authentication Result Names" Registry Description
6.6. 「メール認証結果名」レジストリの説明

Names of message authentication result codes supported by this specification must be registered with IANA, with the exception of experimental codes as described in Section 2.7.7.


New entries are assigned only for values that have received Expert Review, per [IANA-CONSIDERATIONS]. The designated expert shall be appointed by the IESG. The designated expert has discretion to request that a publication be referenced if a clear, concise definition of the authentication result cannot be provided, such that interoperability is assured. Registrations should otherwise be permitted. The designated expert can also handle requests to mark any current registration as "deprecated".


No two entries can have the same combination of method and code.


An entry in this registry contains the following:


Auth Method: an authentication method for which results are being returned using the header field defined in this document.


Code: a result code that can be returned for this authentication method.


Specification: either free-form text explaining the meaning of this method-code combination or a reference to such a definition.


Status: the status of this entry, which is one of the following:


active: The entry is in current use.


deprecated: The entry is no longer in current use.


6.7. "Email Authentication Result Names" Registry Update
6.7. 「メール認証結果名」レジストリの更新

For the following entries in this registry, the new "Specification" field has been set as follows:


o All "auth" method result codes ("fail", "none", "pass", "permerror", and "temperror") are now specified in Section 2.7.4 of this document.

o すべての「auth」メソッドの結果コード(「fail」、「none」、「pass」、「permerror」、および「temperror」)は、このドキュメントのセクション2.7.4で指定されています。

o All "dkim" method result names ("fail", "neutral", "none", "pass", "permerror", "policy", and "temperror") are now specified in Section 2.7.1 of this document.

o すべての「dkim」メソッドの結果名(「fail」、「neutral」、「none」、「pass」、「permerror」、「policy」、および「temperror」)は、このドキュメントのセクション2.7.1で指定されています。

o All "iprev" method result names ("fail", "pass", "permerror", and "temperror") are now specified in Section 2.7.3 of this document.

o すべての「iprev」メソッドの結果名(「fail」、「pass」、「permerror」、および「temperror」)は、このドキュメントのセクション2.7.3で指定されています。

o The "spf" method result names "fail", "neutral", "none", "pass", "permerror", "policy", "softfail", and "temperror" are now specified in Section 2.7.2 of this document. The registration for result name "hardfail" is not updated.

o 「spf」メソッドの結果名「fail」、「neutral」、「none」、「pass」、「permerror」、「policy」、「softfail」、および「temperror」は、このドキュメントのセクション2.7.2で指定されています。 。結果名「hardfail」の登録は更新されません。

The following entries in this registry have been updated with a new "Status" field set to "deprecated", and with no change to the "Specification" field as they reference historic protocols:


o All "domainkeys" method result names ("fail", "neutral", "none", "pass", "permerror", "policy", and "temperror").

o すべての「domainkeys」メソッドの結果名(「fail」、「neutral」、「none」、「pass」、「permerror」、「policy」、および「temperror」)。

o All "sender-id" method result names ("fail", "neutral", "none", "pass", "permerror", "policy", "softfail", and "temperror").

o すべての「sender-id」メソッドの結果名(「fail」、「neutral」、「none」、「pass」、「permerror」、「policy」、「softfail」、および「temperror」)。

6.8. SMTP Enhanced Status Codes
6.8. SMTP拡張ステータスコード

The entry for X.7.25 in the "Enumerated Status Codes" subregistry of the "Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes Registry" has been updated to refer only to Section 3.3 of [AUTH-ESC], as that is where that registration was done.


7. Security Considerations
7. セキュリティに関する考慮事項

The following security considerations apply when adding or processing the Authentication-Results header field:


7.1. Forged Header Fields
7.1. 偽造ヘッダーフィールド

An MTA not applying the filtering discussed in Section 5 exposes MUAs to false conclusions based on forged header fields. A malicious user or agent could forge a header field using the DNS domain of a receiving ADMD as the authserv-id token in the value of the header field and, with the rest of the value, claim that the message was properly authenticated. The non-conformant MTA would fail to strip the forged header field, and the MUA could inappropriately trust it.


For this reason, it is best not to have processing of the Authentication-Results header field enabled by default; instead, it should be ignored, at least for the purposes of enacting filtering decisions, unless specifically enabled by the user or administrator after verifying that the border MTA is compliant. It is acceptable to have an MUA aware of this specification but have an explicit list of hostnames whose Authentication-Results header fields are trustworthy; however, this list should initially be empty.

このため、Authentication-Resultsヘッダーフィールドの処理をデフォルトで有効にしないことをお勧めします。代わりに、境界のMTAが準拠していることを確認した後、ユーザーまたは管理者が特に有効にしない限り、少なくともフィルタリングの決定を行う目的で、これを無視する必要があります。 MUAにこの仕様を認識させることは許容されますが、Authentication-Resultsヘッダーフィールドが信頼できるホスト名の明示的なリストがあります。ただし、このリストは最初は空である必要があります。

Proposed alternative solutions to this problem were made some time ago and are listed below. To date, they have not been developed due to lack of demand but are documented here should the information be useful at some point in the future:


1. Possibly the simplest is a digital signature protecting the header field, such as using [DKIM], that can be verified by an MUA by using a posted public key. Although one of the main purposes of this document is to relieve the burden of doing message authentication work at the MUA, this only requires that the MUA learn a single authentication scheme even if a number of them are in use at the border MTA. Note that [DKIM] requires that the From header field be signed, although in this application, the signing agent (a trusted MTA) likely cannot authenticate that value, so the fact that it is signed should be ignored. Where the authserv-id is the ADMD's domain name, the authserv-id matching this valid internal signature's "d=" DKIM value is sufficient.

1. おそらく最も簡単なのは、[DKIM]を使用するなど、ヘッダーフィールドを保護するデジタル署名であり、投稿された公開鍵を使用してMUAで検証できます。このドキュメントの主な目的の1つはMUAでメッセージ認証作業を行う負担を軽減することですが、これは、境界MTAで複数の認証スキームが使用されている場合でも、MUAが単一の認証スキームを学習することのみを要求します。 [DKIM]ではFromヘッダーフィールドに署名する必要があることに注意してください。ただし、このアプリケーションでは、署名エージェント(信頼できるMTA)はその値を認証できない可能性が高いため、署名されているという事実は無視する必要があります。 authserv-idがADMDのドメイン名である場合、この有効な内部署名の「d = DKIM値」に一致するauthserv-idで十分です。

2. Another would be a means to interrogate the MTA that added the header field to see if it is actually providing any message authentication services and saw the message in question, but this isn't especially palatable given the work required to craft and implement such a scheme.

2. もう1つは、ヘッダーフィールドを追加したMTAに問い合わせて、実際にメッセージ認証サービスを提供しているかどうかを確認し、問題のメッセージを確認する手段ですが、このようなスキームを作成して実装するために必要な作業を考えると、これは特に口当たりが良いものではありません。 。

3. Yet another might be a method to interrogate the internal MTAs that apparently handled the message (based on Received header fields) to determine whether any of them conform to Section 5 of this memo. This, too, has potentially high barriers to entry.

3. さらに別の方法は、メッセージを(Receivedヘッダーフィールドに基づいて)明らかに処理した内部MTAに問い合わせて、このメモのセクション5に準拠しているかどうかを判断する方法かもしれません。これも、参入障壁が高い可能性があります。

4. Extensions to [IMAP], [SMTP], and [POP3] could be defined to allow an MUA or filtering agent to acquire the authserv-id in use within an ADMD, thus allowing it to identify which Authentication-Results header fields it can trust.

4. [IMAP]、[SMTP]、および[POP3]の拡張を定義して、MUAまたはフィルタリングエージェントがADMD内で使用中のauthserv-idを取得できるようにすることで、信頼できるAuthentication-Resultsヘッダーフィールドを識別できるようになります。 。

5. On the presumption that internal MTAs are fully compliant with Section 3.6 of [MAIL] and the compliant internal MTAs are using their own hostnames or the ADMD's DNS domain name as the authserv-id token, this header field should always appear above a Received header added by a trusted MTA. This can be used as a test for header field validity.

5. 内部MTAが[MAIL]のセクション3.6に完全に準拠しており、準拠した内部MTAが独自のホスト名またはADMDのDNSドメイン名をauthserv-idトークンとして使用しているという前提で、このヘッダーフィールドは常に追加された受信ヘッダーの上に表示される必要があります信頼できるMTA。これは、ヘッダーフィールドの有効性のテストとして使用できます。

Support for some of these is being considered for future work.


In any case, a mechanism needs to exist for an MUA or filter to verify that the host that appears to have added the header field (a) actually did so and (b) is legitimately adding that header field for this delivery. Given the variety of messaging environments deployed today, consensus appears to be that specifying a particular mechanism for doing so is not appropriate for this document.


Mitigation of the forged header field attack can also be accomplished by moving the authentication results data into metadata associated with the message. In particular, an SMTP extension [SMTP] could be established to communicate authentication results from the border MTA to intermediate and delivery MTAs; the latter of these could arrange to store the authentication results as metadata retrieved and rendered along with the message by an IMAP client [IMAP] aware of a similar extension in that protocol. The delivery MTA would be told to trust data via this extension only from MTAs it trusts, and border MTAs would not accept data via this extension from any source. There is no vector in such an arrangement for forgery of authentication data by an outside agent.


7.2. Misleading Results
7.2. 誤解を招く結果

Until some form of service for querying the reputation of a sending agent is widely deployed, the existence of this header field indicating a "pass" does not render the message trustworthy. It is possible for an arriving piece of spam or other undesirable mail to pass checks by several of the methods enumerated above (e.g., a piece of spam signed using [DKIM] by the originator of the spam, which


might be a spammer or a compromised system). In particular, this issue is not resolved by forged header field removal (discussed above).


Hence, MUAs and downstream filters must take some care with use of this header even after possibly malicious headers are scrubbed.


7.3. Header Field Position
7.3. ヘッダーフィールドの位置

Despite the requirements of [MAIL], header fields can sometimes be reordered en route by intermediate MTAs. The goal of requiring header field addition only at the top of a message is an acknowledgment that some MTAs do reorder header fields, but most do not. Thus, in the general case, there will be some indication of which MTAs (if any) handled the message after the addition of the header field defined here.


7.4. Reverse IP Query Denial-of-Service Attacks
7.4. リバースIPクエリのサービス拒否攻撃

Section 4.6.4 of [SPF] observes that limits are necessary on recursive evaluations of SPF records in order to avoid abuse of or attacks on the DNS when verifying arriving client connections. A verifier wishing to do this check and report this information needs to take care not to go to unbounded lengths to resolve "A" and "PTR" queries. MUAs or other filters making use of an "iprev" result specified by this document need to be aware of the algorithm used by the verifier reporting the result and, especially, its limitations.


7.5. Mitigation of Backscatter
7.5. 後方散乱の軽減

Failing to follow the instructions of Section 4.2 can result in a denial-of-service attack caused by the generation of DSN messages [DSN] (or equivalent) to addresses that did not send the messages being rejected.


7.6. Internal MTA Lists
7.6. 内部MTAリスト

Section 5 describes a procedure for scrubbing header fields that may contain forged authentication results about a message. A compliant installation will have to include, at each MTA, a list of other MTAs known to be compliant and trustworthy. Failing to keep this list current as internal infrastructure changes may expose an ADMD to attack.


7.7. Attacks against Authentication Methods
7.7. 認証方法に対する攻撃

If an attack against an authentication method becomes known, clearly then the agent verifying that method can be fooled into thinking an inauthentic message is authentic, and thus the value of this header field can be misleading. It follows that any attack against the authentication methods supported by this document is also a security consideration here.


7.8. Intentionally Malformed Header Fields
7.8. 意図的に不正な形式のヘッダーフィールド

As with any other header field found in the message, it is possible for an attacker to add an Authentication-Results header field that is extraordinarily large or otherwise malformed in an attempt to discover or exploit weaknesses in header field parsing code. Implementers must thoroughly verify all such header fields received from MTAs and be robust against intentionally as well as unintentionally malformed header fields.


7.9. Compromised Internal Hosts
7.9. 侵害された内部ホスト

An internal MUA or MTA that has been compromised could generate mail with a forged From header field and a forged Authentication-Results header field that endorses it. Although it is clearly a larger concern to have compromised internal machines than it is to prove the value of this header field, this risk can be mitigated by arranging that internal MTAs will remove this header field if it claims to have been added by a trusted border MTA (as described above), yet the SMTP connection [SMTP] is not coming from an internal machine known to be running an authorized MTA. However, in such a configuration, legitimate MTAs will have to add this header field when legitimate internal-only messages are generated. This is also covered in Section 5.

侵害された内部MUAまたはMTAは、偽造されたFromヘッダーフィールドと偽造されたAuthentication-Resultsヘッダーフィールドを含むメールを生成し、それを承認する可能性があります。このヘッダーフィールドの値を証明することよりも、内部のマシンが危険にさらされていることのほうが明らかに大きな懸念ですが、信頼できる国境によって追加されたと主張する場合、内部のMTAがこのヘッダーフィールドを削除するように調整することで、このリスクを軽減できます。 MTA(上記のとおり)ですが、SMTP接続[SMTP]は、承認されたMTAを実行していることがわかっている内部マシンからのものではありません。ただし、このような構成では、正当なMTAは、正当な内部専用メッセージが生成されたときに、このヘッダーフィールドを追加する必要があります。これについては、セクション5でも説明します。

7.10. Encapsulated Instances
7.10. カプセル化されたインスタンス

MIME messages can contain attachments of type "message/rfc822", which contain other messages. Such an encapsulated message can also contain an Authentication-Results header field. Although the processing of these is outside of the intended scope of this document (see Section 1.3), some simple guidance to MUA developers is appropriate here.

MIMEメッセージには、「message / rfc822」タイプの添付ファイルを含めることができます。これには、他のメッセージが含まれます。このようなカプセル化されたメッセージには、Authentication-Resultsヘッダーフィールドを含めることもできます。これらの処理はこのドキュメントの意図する範囲外ですが(セクション1.3を参照)、MUA開発者への簡単なガイダンスがここでは適切です。

Since MTAs are generally unlikely to strip Authentication-Results header fields during mailbox delivery, normative language exists in Section 4.1 cautioning MUAs to ignore such instances within MIME attachments, as might be included when a message is forwarded. Moreover, when extracting a message digest to separate mail store messages or other media, such header fields should be removed so that they will never be interpreted improperly by MUAs that might later consume them.


There can be cases where these header fields included as part of encapsulated messages might actually be of value, such as when they are taken from messages within the same ADMD where they will be consumed. Caution must be taken to ensure that the consumer fully understands the semantics of what the header field is indicating and the message's handling history before ascribing any value, positive or negative, to such data.


7.11. Reverse Mapping
7.11. 逆マッピング

Although Section 3 of this memo includes explicit support for the "iprev" method, its value as an authentication mechanism is limited. Implementers of both this specification and agents that use the data it relays are encouraged to become familiar with the issues raised by [DNSOP-REVERSE] when deciding whether or not to include support for "iprev".


8. References
8. 参考文献
8.1. Normative References
8.1. 引用文献

[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <>.

[ABNF]クロッカー、D。、エド。およびP. Overell、「構文仕様の拡張BNF:ABNF」、STD 68、RFC 5234、DOI 10.17487 / RFC5234、2008年1月、<>。

[IANA-HEADERS] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, DOI 10.17487/RFC3864, September 2004, <>.

[IANA-HEADERS] Klyne、G.、Nottingham、M。、およびJ. Mogul、「メッセージヘッダーフィールドの登録手順」、BCP 90、RFC 3864、DOI 10.17487 / RFC3864、2004年9月、<https:// www。>。

[MAIL] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008, <>.

[メール] Resnick、P。、編、「インターネットメッセージ形式」、RFC 5322、DOI 10.17487 / RFC5322、2008年10月、<>。

[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, <>.

[MIME] Freed、N。およびN. Borenstein、「Multipurpose Internet Mail Extensions(MIME)Part One:Format of Internet Message Bodies」、RFC 2045、DOI 10.17487 / RFC2045、1996年11月、<https://www.rfc->。

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <>.

[RFC2119] Bradner、S。、「要件レベルを示すためにRFCで使用するキーワード」、BCP 14、RFC 2119、DOI 10.17487 / RFC2119、1997年3月、< rfc2119>。

[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, February 2012, <>.

[RFC6530] Klensin、J。およびY. Ko、「国際化電子メールの概要とフレームワーク」、RFC 6530、DOI 10.17487 / RFC6530、2012年2月、<>。

[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, <>.

[RFC6531] Yao、J。およびW. Mao、「SMTP Extension for Internationalized Email」、RFC 6531、DOI 10.17487 / RFC6531、2012年2月、<>。

[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 2012, <>.

[RFC6532] Yang、A.、Steele、S。、およびN. Freed、「Internationalized Email Headers」、RFC 6532、DOI 10.17487 / RFC6532、2012年2月、< rfc6532>。

[RFC7601] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 7601, DOI 10.17487/RFC7601, August 2015, <>.

[RFC7601] Kucherawy、M。、「メッセージ認証ステータスを示すためのメッセージヘッダーフィールド」、RFC 7601、DOI 10.17487 / RFC7601、2015年8月、<>。

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <>.

[RFC8174] Leiba、B。、「RFC 2119キーワードの大文字と小文字のあいまいさ」、BCP 14、RFC 8174、DOI 10.17487 / RFC8174、2017年5月、< rfc8174>。

[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008, <>.

[SMTP] Klensin、J。、「Simple Mail Transfer Protocol」、RFC 5321、DOI 10.17487 / RFC5321、2008年10月、<>。

8.2. Informative References
8.2. 参考引用

[ADSP] Allman, E., Fenton, J., Delany, M., and J. Levine, "DomainKeys Identified Mail (DKIM) Author Domain Signing Practices (ADSP)", RFC 5617, DOI 10.17487/RFC5617, August 2009, <>.

[ADSP] Allman、E.、Fenton、J.、Delany、M。、およびJ. Levine、「DomainKeys Identified Mail(DKIM)Author Domain Signing Practices(ADSP)」、RFC 5617、DOI 10.17487 / RFC5617、2009年8月、 <>。

[AR-VBR] Kucherawy, M., "Authentication-Results Registration for Vouch by Reference Results", RFC 6212, DOI 10.17487/RFC6212, April 2011, <>.

[AR-VBR] Kucherawy、M。、「Authentication-Results Registration for Vouch by Reference Results」、RFC 6212、DOI 10.17487 / RFC6212、2011年4月、<> 。

[ATPS] Kucherawy, M., "DomainKeys Identified Mail (DKIM) Authorized Third-Party Signatures", RFC 6541, DOI 10.17487/RFC6541, February 2012, <>.

[ATPS] Kucherawy、M。、「DomainKeys Identified Mail(DKIM)Authorized Third-Party Signatures」、RFC 6541、DOI 10.17487 / RFC6541、2012年2月、<> 。

[AUTH] Siemborski, R., Ed. and A. Melnikov, Ed., "SMTP Service Extension for Authentication", RFC 4954, DOI 10.17487/RFC4954, July 2007, <>.

[AUTH] Siemborski、R。、エド。 A. Melnikov編、「認証用のSMTPサービス拡張」、RFC 4954、DOI 10.17487 / RFC4954、2007年7月、<>。

[AUTH-ESC] Kucherawy, M., "Email Authentication Status Codes", RFC 7372, DOI 10.17487/RFC7372, September 2014, <>.

[AUTH-ESC] Kucherawy、M。、「Email Authentication Status Codes」、RFC 7372、DOI 10.17487 / RFC7372、2014年9月、<>。

[DKIM] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, September 2011, <>.

[DKIM] Crocker、D。、編、Hansen、T。、編、M。Kucherawy、編、「DomainKeys Identified Mail(DKIM)Signatures」、STD 76、RFC 6376、DOI 10.17487 / RFC6376、2011年9月、<>。

[DMARC] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, <>.

[DMARC] Kucherawy、M.、Ed。およびE. Zwicky、編、「ドメインベースのメッセージ認証、レポート、および準拠(DMARC)」、RFC 7489、DOI 10.17487 / RFC7489、2015年3月、< rfc7489>。

[DNS] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <>.

[DNS] Mockapetris、P。、「ドメイン名-実装と仕様」、STD 13、RFC 1035、DOI 10.17487 / RFC1035、1987年11月、<>。

[DNS-IP6] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6", STD 88, RFC 3596, DOI 10.17487/RFC3596, October 2003, <>.

[DNS-IP6] Thomson、S.、Huitema、C.、Ksinant、V.、and M. Souissi、 "DNS Extensions to Support IP Version 6"、STD 88、RFC 3596、DOI 10.17487 / RFC3596、October 2003、<>。

[DNSOP-REVERSE] Senie, D. and A. Sullivan, "Considerations for the use of DNS Reverse Mapping", Work in Progress, draft-ietf-dnsop-reverse-mapping-considerations-06, March 2008.

[DNSOP-REVERSE] Senie、D。およびA. Sullivan、「DNSリバースマッピングの使用に関する考慮事項」、作業中、draft-ietf-dnsop-reverse-mapping-considerations-06、2008年3月。

[DOMAINKEYS] Delany, M., "Domain-Based Email Authentication Using Public Keys Advertised in the DNS (DomainKeys)", RFC 4870, DOI 10.17487/RFC4870, May 2007, <>.

[DOMAINKEYS] Delany、M。、「DNS(DomainKeys)でアドバタイズされた公開キーを使用したドメインベースの電子メール認証」、RFC 4870、DOI 10.17487 / RFC4870、2007年5月、< info / rfc4870>。

[DSN] Moore, K. and G. Vaudreuil, "An Extensible Message Format for Delivery Status Notifications", RFC 3464, DOI 10.17487/RFC3464, January 2003, <>.

[DSN] Moore、K。およびG. Vaudreuil、「An Delivery Extensible Message Formats for Delivery Status Notifications」、RFC 3464、DOI 10.17487 / RFC3464、2003年1月、< >。

[EMAIL-ARCH] Crocker, D., "Internet Mail Architecture", RFC 5598, DOI 10.17487/RFC5598, July 2009, <>.

[メールアーク] Crocker、D。、「インターネットメールアーキテクチャ」、RFC 5598、DOI 10.17487 / RFC5598、2009年7月、<>。

[IANA-CONSIDERATIONS] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <>.

[IANA-CONSIDERATIONS] Cotton、M.、Leiba、B。、およびT. Narten、「RFCでIANAの考慮事項セクションを作成するためのガイドライン」、BCP 26、RFC 8126、DOI 10.17487 / RFC8126、2017年6月、<https:/ />。

[IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, <>.

[IMAP] Crispin、M。、「インターネットメッセージアクセスプロトコル-バージョン4rev1」、RFC 3501、DOI 10.17487 / RFC3501、2003年3月、<>。

[POP3] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996, <>.

[POP3]マイヤーズ、J。およびM.ローズ、「Post Office Protocol-Version 3」、STD 53、RFC 1939、DOI 10.17487 / RFC1939、1996年5月、< rfc1939>。

[RFC5451] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 5451, DOI 10.17487/RFC5451, April 2009, <>.

[RFC5451] Kucherawy、M。、「メッセージ認証ステータスを示すためのメッセージヘッダーフィールド」、RFC 5451、DOI 10.17487 / RFC5451、2009年4月、<>。

[RFC6008] Kucherawy, M., "Authentication-Results Registration for Differentiating among Cryptographic Results", RFC 6008, DOI 10.17487/RFC6008, September 2010, <>.

[RFC6008] Kucherawy、M。、「Authentication-Results Registration for Differentiating between Cryptographic Results」、RFC 6008、DOI 10.17487 / RFC6008、2010年9月、<>。

[RFC6577] Kucherawy, M., "Authentication-Results Registration Update for Sender Policy Framework (SPF) Results", RFC 6577, DOI 10.17487/RFC6577, March 2012, <>.

[RFC6577] Kucherawy、M。、「Authentication-Results Registration Update for Sender Policy Framework(SPF)Results」、RFC 6577、DOI 10.17487 / RFC6577、2012年3月、< rfc6577>。

[RFC7001] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 7001, DOI 10.17487/RFC7001, September 2013, <>.

[RFC7001] Kucherawy、M。、「メッセージ認証ステータスを示すためのメッセージヘッダーフィールド」、RFC 7001、DOI 10.17487 / RFC7001、2013年9月、<>。

[RFC7410] Kucherawy, M., "A Property Types Registry for the Authentication-Results Header Field", RFC 7410, DOI 10.17487/RFC7410, December 2014, <>.

[RFC7410] Kucherawy、M。、「Authentication-Resultsヘッダーフィールドのプロパティタイプレジストリ」、RFC 7410、DOI 10.17487 / RFC7410、2014年12月、<> 。

[RFC8301] Kitterman, S., "Cryptographic Algorithm and Key Usage Update to DomainKeys Identified Mail (DKIM)", RFC 8301, DOI 10.17487/RFC8301, January 2018, <>.

[RFC8301] Kitterman、S.、「暗号化アルゴリズムとDomainKeys Identified Mail(DKIM)のキー使用法の更新」、RFC 8301、DOI 10.17487 / RFC8301、2018年1月、< rfc8301>。

[RRVS] Mills, W. and M. Kucherawy, "The Require-Recipient-Valid-Since Header Field and SMTP Service Extension", RFC 7293, DOI 10.17487/RFC7293, July 2014, <>.

[RRVS] Mills、W。およびM. Kucherawy、「The Require-Recipient-Valid-Since Header Field and SMTP Service Extension」、RFC 7293、DOI 10.17487 / RFC7293、2014年7月、<https://www.rfc-editor .org / info / rfc7293>。

[SECURITY] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, DOI 10.17487/RFC3552, July 2003, <>.

[セキュリティ] Rescorla、E。およびB. Korver、「セキュリティに関する考慮事項に関するRFCテキストの作成ガイドライン」、BCP 72、RFC 3552、DOI 10.17487 / RFC3552、2003年7月、< info / rfc3552>。

[SENDERID] Lyon, J. and M. Wong, "Sender ID: Authenticating E-Mail", RFC 4406, DOI 10.17487/RFC4406, April 2006, <>.

[SENDERID] Lyon、J。およびM. Wong、「Sender ID:Authenticating E-Mail」、RFC 4406、DOI 10.17487 / RFC4406、2006年4月、<> 。

[SMIME-REG] Melnikov, A., "Authentication-Results Registration for S/MIME Signature Verification", RFC 7281, DOI 10.17487/RFC7281, June 2014, <>.

[SMIME-REG] Melnikov、A。、「Authentication-Results Registration for S / MIME Signature Verification」、RFC 7281、DOI 10.17487 / RFC7281、2014年6月、< >。

[SPF] Kitterman, S., "Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1", RFC 7208, DOI 10.17487/RFC7208, April 2014, <>.

[SPF]キッターマンS.、「電子メールでのドメインの使用を承認するための送信者ポリシーフレームワーク(SPF)、バージョン1」、RFC 7208、DOI 10.17487 / RFC7208、2014年4月、< / info / rfc7208>。

[VBR] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By Reference", RFC 5518, DOI 10.17487/RFC5518, April 2009, <>.

[VBR] Hoffman、P.、Levine、J。、およびA. Hathcock、「Vouch By Reference」、RFC 5518、DOI 10.17487 / RFC5518、2009年4月、< rfc5518>。

Appendix A. Legacy MUAs

Implementers of this specification should be aware that many MUAs are unlikely to be retrofitted to support the Authentication-Results header field and its semantics. In the interests of convenience and quicker adoption, a delivery MTA might want to consider adding things that are processed by existing MUAs in addition to the Authentication-Results header field. One suggestion is to include a Priority header field, on messages that don't already have such a header field, containing a value that reflects the strength of the authentication that was accomplished, e.g., "low" for weak or no authentication, "normal" or "high" for good or strong authentication.

この仕様の実装者は、Authentication-Resultsヘッダーフィールドとそのセマンティクスをサポートするように多くのMUAが改造される可能性は低いことを認識しておく必要があります。利便性と迅速な採用のために、配信MTAは、Authentication-Resultsヘッダーフィールドに加えて、既存のMUAによって処理されるものを追加することを検討する場合があります。 1つの提案は、Priorityヘッダーフィールドを、そのようなヘッダーフィールドがまだないメッセージに含めることです。これには、達成された認証の強度を反映する値が含まれます。たとえば、「弱い」または「認証なし」、「通常」 "または" high "は、良好または強力な認証を示します。

Some modern MUAs can already filter based on the content of this header field. However, there is keen interest in having MUAs make some kind of graphical representation of this header field's meaning to end users. Until this capability is added (i.e., while this specification and its successors continue to be adopted), other interim means of conveying authentication results may be necessary.


Appendix B. Authentication-Results Examples

This section presents some examples of the use of this header field to indicate authentication results.


B.1. Trivial Case: Header Field Not Present
B.1. 些細なケース:ヘッダーフィールドがありません

The trivial case:


        Received: from
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Hello! Goodbye!


Example 1: Header Field Not Present The Authentication-Results header field is completely absent. The MUA may make no conclusion about the validity of the message. This could be the case because (1) the message authentication services were not available at the time of delivery, (2) no service is provided, or (3) the MTA is not in compliance with this specification.

例1:ヘッダーフィールドが存在しないAuthentication-Resultsヘッダーフィールドは完全にありません。 MUAはメッセージの有効性について結論を下さない場合があります。これは、(1)配信時にメッセージ認証サービスが利用できなかった、(2)サービスが提供されなかった、または(3)MTAがこの仕様に準拠していない場合に発生する可能性があります。

B.2. Nearly Trivial Case: Service Provided, but No Authentication Done
B.2. 些細なケース:サービスは提供されるが、認証は行われない

A message that was delivered by an MTA that conforms to this specification but provides no actual message authentication service:


        Authentication-Results: 1; none
        Received: from
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Hello! Goodbye!


Example 2: Header Present but No Authentication Done


The Authentication-Results header field is present, showing that the delivering MTA conforms to this specification. It used its DNS domain name as the authserv-id. The presence of "none" (and the absence of any method or result tokens) indicates that no message authentication was done. The version number of the specification to which the field's content conforms is explicitly provided.

Authentication-Resultsヘッダーフィールドが表示され、配信するMTAがこの仕様に準拠していることが示されます。 DNSドメイン名をauthserv-idとして使用しました。 「なし」の存在(およびメソッドまたは結果トークンの不在)は、メッセージ認証が行われなかったことを示します。フィールドのコンテンツが準拠する仕様のバージョン番号が明示的に提供されます。

B.3. Service Provided, Authentication Done
B.3. サービス提供、認証完了

A message that was delivered by an MTA that conforms to this specification and applied some message authentication:


        Received: from
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTP id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Hello! Goodbye!


Example 3: Header Reporting Results


The Authentication-Results header field is present, indicating that the border MTA conforms to this specification. The authserv-id is once again the DNS domain name. Furthermore, the message was authenticated by that MTA via the method specified in [SPF]. Note that since that method cannot authenticate the local-part, it has been omitted from the result's value. The MUA could extract and relay this extra information if desired.

Authentication-Resultsヘッダーフィールドが存在し、ボーダーMTAがこの仕様に準拠していることを示します。 authserv-idは、ここでもDNSドメイン名です。さらに、メッセージは[SPF]で指定された方法でMTAによって認証されました。このメソッドはローカル部分を認証できないため、結果の値から省略されていることに注意してください。 MUAは、必要に応じてこの追加情報を抽出して中継できます。

B.4. Service Provided, Several Authentications Done, Single MTA
B.4. サービスの提供、いくつかの認証の完了、単一のMTA

A message that was relayed inbound via a single MTA that conforms to this specification and applied three different message authentication checks:


                  auth=pass (cram-md5);
        Authentication-Results:; iprev=pass
        Received: from (8.11.6/8.11.6)
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTPA id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Hello! Goodbye!


Example 4: Headers Reporting Results from One MTA


The Authentication-Results header field is present, indicating that the delivering MTA conforms to this specification. Once again, the receiving DNS domain name is used as the authserv-id. Furthermore, the sender authenticated themselves to the MTA via a method specified in [AUTH], and both SPF and "iprev" checks were done and passed. The MUA could extract and relay this extra information if desired.

Authentication-Resultsヘッダーフィールドが存在し、配信MTAがこの仕様に準拠していることを示します。ここでも、受信DNSドメイン名がauthserv-idとして使用されます。さらに、送信者は[AUTH]で指定された方法でMTAに自分自身を認証し、SPFと "iprev"の両方のチェックが行われ、渡されました。 MUAは、必要に応じてこの追加情報を抽出して中継できます。

Two Authentication-Results header fields are not required, since the same host did all of the checking. The authenticating agent could have consolidated all the results into one header field.


This example illustrates a scenario in which a remote user on a dial-up connection ( sends mail to a border MTA ( using SMTP authentication to prove identity. The dial-up provider has been explicitly authorized to relay mail as, producing a "pass" result from the SPF check.


B.5. Service Provided, Several Authentications Done, Different MTAs
B.5. 提供されるサービス、いくつかの認証、異なるMTA

A message that was relayed inbound by two different MTAs that conform to this specification and applied multiple message authentication checks:


                  dkim=pass (good signature)
        Received: from
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTP id i7PK0sH7021929;
                  Fri, Feb 15 2002 17:19:22 -0800
        DKIM-Signature:  v=1; a=rsa-sha256; s=gatsby;;
                  t=1188964191; c=simple/simple; h=From:Date:To:Subject:
                  b=EToRSuvUfQVP3Bkz ... rTB0t0gYnBVCM=
                  auth=pass (cram-md5);
        Received: from
                      ( [])
                  by (8.11.6/8.11.6)
                      with ESMTPA id g1G0r1kA003489;
                  Fri, Feb 15 2002 17:19:07 -0800
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Hello! Goodbye!


Example 5: Headers Reporting Results from Multiple MTAs


The Authentication-Results header field is present, indicating conformance to this specification. Once again, the authserv-id used is the recipient's DNS domain name. The header field is present twice because two different MTAs in the chain of delivery did authentication tests. The first MTA,, reports that SMTP AUTH and SPF were both used and that the former passed while the latter failed. In the SMTP AUTH case, additional information is provided in the comment field, which the MUA can choose to render if desired.

Authentication-Resultsヘッダーフィールドが存在し、この仕様への準拠を示しています。ここでも、使用されるauthserv-idは受信者のDNSドメイン名です。配信のチェーン内の2つの異なるMTAが認証テストを行ったため、ヘッダーフィールドは2回存在します。最初のMTAであるmail-router.example.comは、SMTP AUTHとSPFの両方が使用され、前者は成功したが後者は失敗したと報告しています。 SMTP AUTHの場合、コメントフィールドに追加情報が提供され、必要に応じてMUAがレンダリングすることを選択できます。

The second MTA,, reports that it did a DKIM test (which passed). Again, additional data about one of the tests are provided as a comment, which the MUA may choose to render. Also noteworthy here is the fact that there is a DKIM signature added by that assured the integrity of the lower Authentication-Results field.


Since different hosts did the two sets of authentication checks, the header fields cannot be consolidated in this example.


This example illustrates more typical transmission of a message into from a user on a dial-up connection The user appears to be legitimate, as they had a valid password allowing authentication at the border MTA using SMTP AUTH. The SPF test failed, since has not granted's dial-up network authority to relay mail on its behalf. The DKIM test passed because the sending user had a private key matching one of's published public keys and used it to sign the message.

この例は、ダイヤルアップ接続example.net上のユーザーからexample.comへのメッセージのより一般的な送信を示しています。 SMTP AUTHを使用して境界MTAでの認証を可能にする有効なパスワードを持っているため、ユーザーは正当なようです。 example.comがexample.netに代わってメールをリレーするダイアルアップネットワーク権限を付与していないため、SPFテストは失敗しました。 DKIMテストは、送信ユーザーがexample.comの公開された公開鍵のいずれかに一致する秘密鍵を持ち、mail-router.example.comがそれを使用してメッセージに署名したため、合格しました。

B.6. Service Provided, Multi-tiered Authentication Done
B.6. サービス提供、多層認証が完了

A message that had authentication done at various stages, one of which was outside the receiving ADMD:


              dkim=pass reason="good signature"
              dkim=fail reason="bad signature"
        Received: from
                  ( [])
              by (8.11.6/8.11.6)
                  for <>
                  with ESMTP id i7PK0sH7021929;
              Fri, Feb 15 2002 17:19:22 -0800
        DKIM-Signature: v=1; a=rsa-sha256; s=furble;
    ; t=1188964198; c=relaxed/simple;
              b=oINEO8hgn/gnunsg ... 9n9ODSNFSDij3=
              dkim=pass (good signature)
        Received: from
                  ( [])
              by (8.11.6/8.11.6)
                  with ESMTP id g1G0r1kA003489;
              Fri, Feb 15 2002 17:19:07 -0800
        DKIM-Signature: v=1; a=rsa-sha256; s=gatsby;
              t=1188964191; c=simple/simple;
              b=EToRSuvUfQVP3Bkz ... rTB0t0gYnBVCM=
        Date: Fri, Feb 15 2002 16:54:30 -0800
        Message-Id: <>
        Subject: here's a sample

Example 6: Headers Reporting Results from Multiple MTAs in Different ADMDs


In this example, we see multi-tiered authentication with an extended trust boundary.


The message was sent from someone at's New York office ( to a mailing list managed at an intermediary. The message was signed at the origin using DKIM.


The message was sent to a mailing list service provider called "", which is used by There, is expanded to a long list of recipients, one of whom is at the Chicago office. In this example, we will assume that the trust boundary for includes the mailing list server at

メッセージは、example.comによって使用される「」と呼ばれるメーリングリストサービスプロバイダーに送信されました。そこでは、meetings @ example.netは、シカゴのオフィスにいる受信者の長いリストに拡張されます。この例では、chicago.example.comの信頼境界にexample.netのメーリングリストサーバーが含まれていると想定します。

The mailing list server there first authenticated the message and affixed an Authentication-Results header field indicating such using its DNS domain name for the authserv-id. It then altered the message by affixing some footer text to the body, including some administrivia such as unsubscription instructions. Finally, the mailing list server affixes a second DKIM signature and begins distribution of the message.


The border MTA for explicitly trusts results from, so that header field is not removed. It performs evaluation of both signatures and determines that the first (most recent) is a "pass" but, because of the aforementioned modifications, the second is a "fail". However, the first signature included the Authentication-Results header added at that validated the second signature. Thus, indirectly, it can be determined that the authentications claimed by both signatures are indeed valid.


Note that two styles of presenting metadata about the result are in use here. In one case, the "reason=" clause is present, which is intended for easy extraction by parsers; in the other case, the CFWS production of the ABNF is used to include such data as a header field comment. The latter can be harder for parsers to extract given the varied supported syntaxes of mail header fields.

ここでは、結果に関するメタデータを提示する2つのスタイルが使用されています。 1つのケースでは、「reason =」句が存在しますが、これはパーサーによる簡単な抽出を目的としています。その他の場合、ABNFのCFWSプロダクションは、ヘッダーフィールドコメントなどのデータを含めるために使用されます。後者は、サポートされているメールヘッダーフィールドのさまざまな構文を考えると、パーサーが抽出するのが難しい場合があります。

B.7. Comment-Heavy Example
B.7. コメントが多い例

The formal syntax permits comments within the content in a number of places. For the sake of illustration, this example is also legal:


       Authentication-Results: (foobar) 1 (baz);
           dkim (Because I like it) / 1 (One yay) = (wait for it) fail
             policy (A dot can go here) . (like that) expired
             (this surprised me) = (as I wasn't expecting it) 1362471462

Example 7: A Very Comment-Heavy but Perfectly Legal Example


Appendix C. Operational Considerations about Message Authentication

Implementation of the Authentication-Results header field is predicated on the idea that authentication (and presumably in the future, reputation) work is typically done by border MTAs rather than MUAs or intermediate MTAs; the latter merely make use of the results determined by the former. Certainly this is not mandatory for participation in electronic mail or message authentication, but this header field and its deployment to date are based on that model. The assumption satisfies several common ADMD requirements:


1. Service operators prefer to resolve the handling of problem messages as close to the border of the ADMD as possible. This enables, for example, rejection of messages at the SMTP level rather than generating a DSN internally. Thus, doing any of the authentication or reputation work exclusively at the MUA or intermediate MTA renders this desire unattainable.

1. サービスオペレーターは、問題のメッセージの処理をADMDの境界のできるだけ近くで解決することを好みます。これにより、たとえば、内部でDSNを生成するのではなく、SMTPレベルでメッセージを拒否できます。したがって、MUAまたは中間MTAで排他的に認証またはレピュテーション作業を行うと、この要望が達成できなくなります。

2. Border MTAs are more likely to have direct access to external sources of authentication or reputation information, since modern MUAs inside of an ADMD are more likely to be heavily firewalled. Thus, some MUAs might not even be able to complete the task of performing authentication or reputation evaluations without complex proxy configurations or similar burdens.

2. ADMD内の最新のMUAは非常にファイアウォールで保護されている可能性が高いため、境界MTAは認証またはレピュテーション情報の外部ソースに直接アクセスする可能性が高くなります。したがって、一部のMUAは、複雑なプロキシ構成または同様の負担なしに、認証またはレピュテーション評価を実行するタスクを完了できない場合もあります。

3. MUAs rely upon the upstream MTAs within their trust boundaries to make correct (as much as is possible) evaluations about the message's envelope, header, and content. Thus, MUAs don't need to know how to do the work that upstream MTAs do; they only need the results of that work.

3. MUAは、信頼境界内のアップストリームMTAに依存して、メッセージのエンベロープ、ヘッダー、およびコンテンツに関する正確な(可能な限り)評価を行います。したがって、MUAは上流のMTAが行う作業の方法を知る必要はありません。彼らはその仕事の結果だけを必要とします。

4. Evaluations about the quality of a message, from simple token matching (e.g., a list of preferred DNS domains) to cryptographic verification (e.g., public/private key work), do have a cost and thus need to be minimized. To that end, performing those tests at the border MTA is far preferred to doing that work at each MUA that handles a message. If an ADMD's environment adheres to common messaging protocols, a reputation query or an authentication check performed by a border MTA would return the same result as the same query performed by an MUA. By contrast, in an environment where the MUA does the work, a message arriving for multiple recipients would thus cause authentication or reputation evaluation to be done more than once for the same message (i.e., at each MUA), causing needless amplification of resource use and creating a possible denial-of-service attack vector.

4. 単純なトークン照合(優先DNSドメインのリストなど)から暗号検証(公開/秘密鍵の作業など)まで、メッセージの品質に関する評価にはコストがかかるため、最小限に抑える必要があります。そのため、境界MTAでこれらのテストを実行することは、メッセージを処理する各MUAでその作業を実行するよりもはるかに優先されます。 ADMDの環境が一般的なメッセージングプロトコルに準拠している場合、境界MTAによって実行されるレピュテーションクエリまたは認証チェックは、MUAによって実行される同じクエリと同じ結果を返します。対照的に、MUAが機能する環境では、複数の受信者に到着するメッセージにより、同じメッセージに対して(つまり、各MUAで)認証またはレピュテーション評価が複数回実行され、リソース使用の不必要な増幅が発生します。そして、起こり得るサービス拒否攻撃ベクトルを作成します。

5. Minimizing change is good. As new authentication and reputation methods emerge, the list of methods supported by this header field would presumably be extended. If MUAs simply consume the contents of this header field rather than actually attempt to do authentication and/or reputation work, then MUAs only need to learn to parse this header field once; emergence of new methods requires only a configuration change at the MUAs and software changes at the MTAs (which are presumably fewer in number). When choosing to implement these functions in MTAs vs. MUAs, the issues of individual flexibility, infrastructure inertia, and scale of effort must be considered. It is typically easier to change a single MUA than an MTA because the modification affects fewer users and can be pursued with less care. However, changing many MUAs is more effort than changing a smaller number of MTAs.

5. 変更を最小限に抑えるのは良いことです。新しい認証およびレピュテーションメソッドが出現すると、このヘッダーフィールドでサポートされるメソッドのリストが拡張されると考えられます。 MUAが実際に認証やレピュテーション作業を行うのではなく、単にこのヘッダーフィールドのコンテンツを使用する場合、MUAはこのヘッダーフィールドの解析を一度だけ学習する必要があります。新しいメソッドの出現には、MUAでの設定変更とMTAでのソフトウェア変更(おそらく数が少ない)のみが必要です。 MTAとMUAでこれらの機能を実装することを選択するときは、個々の柔軟性、インフラストラクチャの慣性、および作業の規模の問題を考慮する必要があります。変更の影響を受けるユーザーが少なく、注意を払うことなく実行できるため、通常はMTAよりも1つのMUAを変更する方が簡単です。ただし、多くのMUAを変更する方が、少数のMTAを変更するよりも労力がかかります。

6. For decisions affecting message delivery and display, assessment based on authentication and reputation is best performed close to the time of message transit, as a message makes its journey toward a user's inbox, not afterwards. DKIM keys, IP address reputations, etc., can change over time or even become invalid, and users can take a long time to read a message once delivered. The value of this work thus degrades, perhaps quickly, once the delivery process has completed. This seriously diminishes the value of this work when done elsewhere than at MTAs.

6. メッセージの配信と表示に影響を与える決定については、メッセージがユーザーの受信トレイに向かって移動するため、メッセージの通過時間の近くで認証とレピュテーションに基づく評価を行うのが最適です。 DKIMキー、IPアドレスのレピュテーションなどは、時間の経過とともに変化したり、無効になったりする可能性があり、ユーザーは配信されたメッセージを読むのに長時間かかる場合があります。したがって、配信プロセスが完了すると、この作業の価値はおそらく急速に低下します。これにより、MTA以外の場所でこの作業を行う場合の価値が大幅に低下します。

Many operational choices are possible within an ADMD, including the venue for performing authentication and/or reputation assessment. The current specification does not dictate any of those choices. Rather, it facilitates those cases in which information produced by one stage of analysis needs to be transported with the message to the next stage.


Appendix D. Changes since RFC 7601
付録D. RFC 7601以降の変更

o Added IANA registration for DKIM "a" and "s" properties.

o DKIM "a"および "s"プロパティのIANA登録を追加しました。

o Included EAI guidance.

o EAIガイダンスが含まれています。

o Adjusted some ABNF tokens and names for easier inclusion by other documents.

o 他のドキュメントに簡単に含めることができるように、いくつかのABNFトークンと名前を調整しました。

o Made minor editorial adjustments.

o 編集の微調整を行いました。

o Deprecated entries from RFCs that are now Historic.

o 現在は歴史的であるRFCからの非推奨のエントリ。

o Erratum 4671 resolved.

o Erratum 4671は解決されました。

o Erratum 5435 resolved.

o エラータ5435が解決されました。



The author wishes to acknowledge the following individuals for their review and constructive criticism of this document: Kurt Andersen, Seth Blank, Tim Draegen, Scott Kitterman, John Levine, and Alessandro Vesely.


Author's Address


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

マレーS.クチェラウィ270アップランドドライブサンフランシスコ、CA 94127アメリカ合衆国