DMARC Working Group K. Andersen
Internet-Draft LinkedIn
Intended status: Experimental B. Long, Ed.
Expires: July 26, 2018 Google
S. Jones, Ed.
TDP
S. Blank, Ed.
ValiMail
M. Kucherawy, Ed.
TDP
January 22, 2018

Authenticated Received Chain (ARC) Protocol
draft-ietf-dmarc-arc-protocol-11

Abstract

The Authenticated Received Chain (ARC) protocol creates a mechanism whereby a series of handlers of an email message can conduct authentication of the email message as it passes among them on the way to its destination, and record the status of that authentication at each step along the handling path, for use by the final recipient in making choices about the disposition of the message. Changes in the message that might break DKIM or DMARC can be identified through the ARC set of header fields.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on July 26, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) 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.


Table of Contents

1. Introduction

Modern email authentication techniques such as the Sender Policy Framework (SPF) [RFC7208] and DomainKeys Identified Mail (DKIM) [RFC6376] have become common.
However, their end-to-end utility is limited by the effects of intermediaries along the transmission path, which either are not listed (for SPF) or which break digital signatures (for DKIM). These issues are described in substantial detail in those protocols’ defining documents as well as in [RFC6377] and [RFC7960].

Technologies that build upon the use of SPF and DKIM can reduce the success of fraudulent email campaigns. To this end, Domain-based Mail Authentication, Reporting and Compliance (DMARC) [RFC7489], validates the domain of the RFC5322.From author header field. However its use along email transmission paths that have independent intermediaries, such as some forwarders and essentially all mailing list services, produces false positive rejections that are problematic, both for the message authors, the intermediary service(s), and for those they are interacting with.

What is needed is a mechanism by which legitimate alteration of a message, which invalidates associated SPF and DKIM information, does not ultimately result in a rejection of an email message on delivery.
Authenticated Receive Chain (ARC) builds upon DKIM mechanisms to provide a sequence of signatures that are more survivable than DKIM’s and that provide a view of the handling sequence for a message, especially the points where alterations of the content might have occurred. Equipped with this more complete information, the recipient system(s) can make a more informed handling choice, reducing or eliminating the false negatives inherent in use of DKIM and/or SPF themselves.

2. Overview

In DKIM, every participating signing agent attaches a signature that is based on the some of the content of the message, local policy, and the domain name of the participating Administrative Management Domain (ADMD). Any verifier can process such a signature; a verified signature means that the domain referenced in the DKIM-Signture’s “d=” parameter has some responsibility for handling the message. An artifact of using digital signature technology for this means that verification also ensures that the message content that was “covered” by the signature has not been altered since the signature was applied. The signatures themselves are generally independent of one another.

By contrast, an ARC signature conveys the following pieces of information:

  1. An assertion that, at the time that the intermediary ADMD processed the message, the various assertions (DKIM-Signature(s) and/or ARC sets) already attached to the message by other ADMDs were or were not valid;
  2. As with DKIM, an assertion that, for a validated signature, the domain name in the signature takes some responsibility for handling of the message and that the message is unchanged since that signature was applied;
  3. A further assertion that binds the ARC evaluation results into the ARC chain sequence.

This protocol accomplishes each of these by adding a new header field to the message for each of these pieces of information, as follows:

A distinguishing feature of all of these is that an ARC participant always adds all of them before relaying a message to the next handling agent en route to its destination. Moreover, as described in Section 5.1, they each have an “instance” number that increases with each ADMD in the handling chain so that their original order can be preserved and the three related header fields can be processed as a group.

3. Definitions and Terminology

This section defines terms used in the rest of the document.

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

Because many of the core concepts and definitions are found in [RFC5598], readers SHOULD to be familiar with the contents of [RFC5598], and in particular, the potential roles of intermediaries in the delivery of email.

Syntax descriptions use Augmented BNF (ABNF) [RFC5234].

3.1. Referenced Definitions

The following terms are defined in other RFCs. Those definitions can be found as follows:

The three header fields that are part of this specification borrow heavily from existing specifications. Rather than repeating all of the formal definitions that are being reused in ARC, this document only describes and specifies changes in syntax and semantics.

Language, syntax, and other details are imported from DKIM [RFC6376]. Specific references can be found below.

4. Protocol Elements and Features

As with other domain authentication technologies (such as SPF, DKIM, and DMARC), ARC makes no claims about the contents of the email message it has sealed. However, for a valid and passing ARC chain, a Final Receiver is able to ascertain:

Given this information, a Final Receiver is able to make a more-informed local policy decision regarding message delivery to the end user in spite of a DMARC failure.

Every participant in an ARC chain, except for the originating sender and Final Receiver, is both an ARC Validator (when receiving) and then an ARC Sealer (when sending a message onward). The validated chain status as determined at message receipt must be passed to the sealer function in order for sealing to occur properly; how this is done is considered ADMD-specific and an implementation detail.

INFORMATIONAL: It is important to understand that validating and then immediately sealing a message leaves no room for message modification, and many early implementations of ARC did not initially work because both operations were performed in a single pass over the message.

4.1. Features of the ARC Protocol

The following protocol features are functional parts and design decisions related the protocol that are not specific to either Validators or Sealers, but ensure the ARC chain conveys this information to a Final Receiver.

4.1.1. Chain of Custody

At a high level, an ARC chain represents a chain of custody of authentication and other trace information (AAR) related to a message, signed by each handler of the message. Each link in the chain (AMS) is designed to be brittle, insofar as it survives only until the next modification of the message. However, the sequence of intermediaries in the handling chain (AS) is designed to remain intact over the entirety of the chain.

The ARC chain can be conceptualized through an analogy with the chain of custody for legal evidence. The material evidence itself is sealed within an tamper-proof bag (AMS) each time. When handed to a new party, that party both vouches for the state of the received evidence container (AAR) and signs for the evidence on a chain of custody report form (AS). As with all analogies, this one should not be taken to interpretive extremes, but primarily used as a conceptual framework.

An ARC chain that is valid and passing has the attributes listed above in Section 4.

Recipients of an ARC chain that is invalid or does not pass SHOULD NOT draw negative conclusions without a good understanding of the wider handling context. Until ARC usage is widespread, intermediaries will continue to modify messages without ARC seals. As with a failing DKIM signature ([RFC6376] Section-6.3), a failing ARC chain SHOULD be treated the same as a message with no ARC chain. [[ NOTE TO WORKING GROUP: This paragraph probably is better placed in Verifier actions. ]]

4.1.2. Optional Participation

Validating an existing chain and then adding your own ARC set to a message allows you to claim responsibility for hanndling the message and modifications, if any, done by your ADMD to benefit message delivery downstream. However, no ADMD is obligated to perform these actions.

4.1.3. Only one ARC Chain (One Chain to Rule Them All)

A message can have only one ARC chain on it at a time (see Section 5.1). Once broken, the chain cannot be restarted, as the chain of custody is no longer valid and responsibility for the message has been lost.

4.1.4. All Failures are Permanent

Because ARC chains are transmitted across multiple intermediaries, all errors, even temporary ones, become unrecoverable and are considered permanent.

Any error validating or sealing a chain, for whatever reason, MUST result in a “cv=fail” verdict.

4.1.5. Benign nature of an ARC Set

Even when an ARC chain is valid and passes, its value is limited to very specific cases. An ARC chain is specifically designed to provide value to a Final Receiver evaluating message delivery in the context of a DMARC failure. An ARC chain in general, and each ARC set in particular, provide additional information, and otherwise is benign. Specifically:

INFORMATIONAL: If an ADMD is unsure whether it will be re-emitting and/or modifying a message, it may elect to seal all inbound mail. For complex or nested ADMD relationships such as found in some hosted mail solutions, this “inbound seal” can be used to facilitate traversal of internal boundaries as well as properly conveying incoming state to any egress MTAs that may need to assert a seal upon exit from the ADMD. Since these internal relationships are highly implementation dependent, this protocol definition can not usefully explore such usage except to note that it is intentionally allowed within the scope of this specification.

4.1.6. Key Management

The public keys for ARC header fields follow the same requirements, syntax and semantics as those for DKIM signatures, described in Section 3.6 of [RFC6376]. ARC places no requirements on the selectors and/or domains used for the ARC header field signatures.

4.1.7. Trace Information

ARC includes trace information encoded in the AAR. While section Section 5.2 defines what information must be provided, sealing ADMDs may provide additional information, and validating receivers may use or ignore this trace information as they wish.

4.1.8. Instance Tags

See section Section 5.1

4.1.9. Chain Validation Status

See section Section 5.4.1

5. The ARC Header Fields

5.1. Instance (‘i=’) Tag

The header fields comprising a single ARC set are identified by the presence of a string in the value portion of the header field that complies with the “tag-spec” ABNF found in Section 3.2 of [RFC6376]. The tag-name is “i” and the value is the text representation of a positive integer, indicating the position in the ARC sequence this set occupies, where the first ARC set is numbered 1. In ABNF terms:

   instance = [FWS] %x69 [FWS] "=" [FWS] position [FWS] ";"
   position = 1*2DIGIT ; 1 - 50

Valid ARC sets must have exactly one instance of each header field for a given position value and signing algorithm. (Initial development of ARC is only being done with a single allowed signing algorithm, but parallel work in the DCRUP working group (https://datatracker.ietf.org/wg/dcrup/about/) is expanding that. For handling multiple signing algorithms, see [ARC-MULTI].)

Because the AMS and AS header field values are made up of tag-spec constructs, the i= tag may be found anywhere within the header field value, but is represented throughout this spec in the initial position for convenience. Implementers are encouraged to place the i= tag at the beginning of the field value to facilitate human inspection of the headers.

5.1.1. Valid Range for Instance Tags

The ‘i’ tag value can range from 1-50 (inclusive).

ARC implementations MUST support at least ten (10) ARC sets.

An effective operational maximum will have to be developed through deployment experience in the field and will be documented within [ARC-USAGE] once determined.

ARC chains with more than the defined operational maximum count MUST be marked with “cv=fail”.

5.2. ARC-Authentication-Results (AAR)

The ARC-Authentication-Results header field is syntactically and semantically identical to an Authentication-Results header field (defined in Section 2.2 of [RFC7601] (A-R)), except that several optional data fields SHOULD be added. ([[ NOTE: these optional data fields are being proposed as amendments to [RFC7601] through a “bis” process. Depending on the sequencing for this specification and said “7601bis” work, it may be possible to drop the noted sections from this specification. ]]) The first element (“Authentication-Results:”) in authres-header is replaced with arc-authres-prefix as follows:

arc-authres-header-prefix = "ARC-Authentication-Results:" [CFWS] arc-info
arc-info = instance *([CFWS] propspec) [CFWS] “;”

The purpose of this header field is to transmit the results of any authentication done on the message upstream to participating ADMDs validating and continuing the chain.

The AAR MUST contain all A-R results from within the participating ADMD, regardless of how many A-R headers are on the message.

5.2.1. ptypes and properties for arc-info

[[ NOTE: This section is being proposed as an amendment to [RFC7601] through a “bis” process. Depending on the sequencing for this specification and said “7601bis” work, it may be possible to this section from this specification. ]]

Certain information pertinent to ascertaining message disposition can be lost in transit when messages are handled by intermediaries. For example, failing DKIM signatures are sometimes removed by MTAs, and most DKIM signatures on messages modified by intermediaries will fail.

The AAR, through these ptype-properties stamped in arc-info, provide a mechanism for this information to survive transit.

The ptypes and properties defined in this section SHOULD be stamped in the AAR:

5.3. ARC-Message-Signature (AMS)

The ARC-Message-Signature header field is syntactically and semantically identical to a DKIM-Signature header field [RFC6376], with the following exceptions:

ARC-Seal header fields MUST NOT be included in the content covered by the signature in this header field.

The AMS SHOULD include any DKIM-Signature header fields already present on the message in the header fields covered by this signature.

The AMS header field MAY include (sign) the AAR header field(s).

Authentication-Results header fields SHOULD NOT be included since they are likely to be deleted by downstream ADMDs (per Section XXX of [RFC7601]), thereby breaking the AMS signature.

As with a DKIM-Signature, the purpose of this header field is to allow the ADMD generating it to take some responsibility for handling this message as it progresses toward delivery.

5.4. ARC-Seal (AS)

The ARC-Seal header field is syntactically and semantically similar to a DKIM-Signature field, with the following exceptions:

5.4.1. The ‘cv’ Tag

A new tag “cv” (chain validation) indicates the the outcome of evaluating the existing ARC chain upon arrival at the ADMD that is adding this header field. It accepts one of three possible values:

In ABNF terms:

 seal-cv-tag = %x63.76 [FWS] "=" [FWS] ("none" / "fail" / "pass")

5.4.2. Implicit Header Fields

The ARC-Seal signs a canonicalized form of the ARC set header values. The ARC set header values are compiled in increasing instance order, starting at 1, and inclue the set being added at the time of sealing the message.

Within a set, the header fields are listed in the following order:

  1. ARC-Authentication-Results
  2. ARC-Message-Signature
  3. ARC-Seal

Where the ARC-Seal is the one being generated, it is input to the hash function in its final form except with an empty “b=” value, in the same manner by which a DKIM-Signature signs itself.

Note that the signing scope for the ARC-Seal is modified in the situation where a chain has failed validation (see Section 7.1).

6. Verifier Actions

A verifier takes the following steps to determine the state of the ARC chain on a message (cv value). Canonicalization, hash functions, and signature validation methods are imported from Section 5 of [RFC6376].

[[ Note: need markdown flag to have subordinate numbering distinction ]]

  1. Collect all ARC sets currently on the message. If there were none, the ARC state is “none” and the algorithm stops here.
  2. If the form of any ARC set is invalid (e.g., does not contain exactly one of each of the three ARC-specific header fields), then the chain state is “fail” and the algorithm stops here.
    1. To avoid the overhead of unnecessary computation and delay from crypto and DNS operations, the cv value for all ARC-Seal(s) MAY be checked at this point. If any of the values are “fail”, then the overall state of the chain is “fail” and the algorithm stops here.
  3. Conduct verification of the ARC-Message-Signature header field bearing the highest instance number. If this verification fails, then the chain state is “fail” and the algorithm stops here.
  4. For each ARC-Seal from the “N”th instance to the first, apply the following logic:
    1. If the value of the “cv” tag on that seal is “fail”, the chain state is “fail” and the algorithm stops here. (This step SHOULD be skipped if the earlier step (2.1) was performed)
    2. In Boolean nomenclature: if ((i == 1 && cv != “none”) or (cv == “none” && i != 1)) then the chain state is “fail” and the algorithm stops here (note that the ordering of the logic is structured for short-circuit evaluation).
    3. Initialize a hash function corresponding to the “a” tag of the ARC-Seal.
    4. Compute the canonicalized form of the ARC header fields, in the order described in Section 5.4.2, using the “relaxed” header canonicalization defined in Section 3.4.2 of [RFC6376]. Pass the canonicalized result to the hash function.
    5. Retrieve the final digest from the hash function.
    6. Retrieve the public key identified by the “s” and “d” tags in the ARC-Seal, as described in Section 4.1.6.
    7. Determine whether the signature portion (“b” tag) of the ARC-Seal and the digest computed above are valid according to the public key. (See also Section Section 6.1 for failure case handling)
    8. If the signature is not valid, the chain state is “fail” and the algorithm stops here.
  5. If all seals pass validation, then the chain state is “pass”, and the algorithm is complete.

[[ Note from Dave: possibly delete the following paragraph as it is more usage/procedural than specification guidance.

KA: It was added to clarify the separation of the verification and signing steps as some of the initial implementations failed to realize that they were not necessarily done in one fell swoop.

KA (v-10): With the addition of the {protocol-elements} section, does the WG think that this can be reasonably removed from this location? ]]

The verifier should save the cv state for subsequent use by any sealing which may be done later (potentially after message modification) within the same trust boundary. The cv state may be recorded by sealing at the time of verification in an initial ARC set (for the ADMD) or may be recorded out of band depending on the architecture of the ADMD.

6.1. Handling DNS Problems While Validating ARC

DNS-based failures to verify a chain are treated no differently than any other ARC violation. They result in a “cv=fail” verdict.

6.2. Responding to ARC Validity Violations During the SMTP Transaction

If a receiver determines that the ARC chain has failed, the receiver MAY signal the breakage through the extended SMTP response code 5.7.7 [RFC3463] “message integrity failure” [ENHANCED-STATUS] and corresponding SMTP response code.

7. Signer Actions

[[ Note from Dave: This seems more like implementation guidance than specification detail. KA: see explanation just above referring to the previous note. ]]

This section includes a specification of the actions an ARC signer takes when presented with a message.

The signer MUST undertake the following steps:

  1. Before creating an ARC signature, perform any other, normal authentication and/or signing, so that the ARC signature can cover those results.
  2. Build and attach the new ARC set:
    1. If an ARC chain exists on the message, then set “N” equal to the highest instance number found on the chain (i=); otherwise set “N” equal to zero for the following steps.
    2. Generate and attach to the message an ARC-Authentication-Results header field using instance number N+1 and the same content from the previous step.
    3. Generate and attach to the message an ARC-Message-Signature header field as defined in Section 5.3 above, using instance number N+1.
    4. Generate and attach to the message an ARC-Seal header field using the general algorithm described in Section 5.4 above, the chain validation status as determined in Section 6, and instance number N+1.

7.1. Marking and Sealing “cv=fail” (Invalid) Chains

The header fields signed by the AS header field b= value in the case of a chain failure MUST be only the matching ‘i=’ instance headers created by the MTA which detected the malformed chain, as if this newest ARC set was the only set present.

8. Usage of ARC and Chain Validity

8.1. Relationship between DKIM-Signature and AMS signing scopes

[[ SB-11: replace with “ARC MUST be the last signer of the message; otherwise it cannot be validated on receipt.” in the signer actions section. KA: Concern that this still does not address the risk of DKIM-Signatures covering ARC chains. This does not seem like it fits in this section but it needs to go somewhere. ]]

DKIM-Signatures SHOULD never sign any ARC header fields.

[[ KA: Response to Dave’s concern: If DKIM covers ARC and ARC covers DKIM, which comes first? The chicken or the egg? I’m open to alternate ways to phrase this without opening the “modifying the DKIM spec” can of worms. ]]

8.2. Assessing Chain Validity Violations

[[ SB-11: move to protocol elements

KA: This seems a bit banal. I suspect that what receivers want is a section on using ARC to override DMARC failures. Would that be to brazen to insert here instead? Or do we relegate that to the [ARC-USAGE] doc? ]]

Email transit can produce broken signatures for a wide variety of benign reasons. This includes possibly breaking one or more ARC signatures. Therefore, receivers need to be wary of ascribing motive to such breakage although patterns of common behaviour may provide some basis for adjusting local policy decisions.

ARC does not attempt to protect an entire message. There are various ways that a message can still be problematic, in spite of having a valid ARC chain. Consequently, all normal, content-based analysis SHOULD still be performed on any message having a valid chain of ARC header sets.

9. Recording and Reporting the Results of ARC Evaluation

The evaluation of an ARC chain provides information which will be useful to both the receiver (or intermediary) and to the initial sender of the message. This information should be preserved and reported as follows.

9.1. Information from an ARC Evaluation

The evaluation of an ARC chain produces a list of domain names for participating intermediaries which handled the message, to wit:

In the case of a failed chain, only the terminal ARC set is covered by the ARC-Seal so the reporting is limited to the findings in that terminal ARC set.

9.2. Recording (local) ARC Evaluation Results

Receivers MAY add an “arc=[pass|fail|policy]” method annotation into a locally-affixed Authentication-Results [RFC7601] header field along with any salient comment(s).

Details of the ARC chain which was evaluated should be included in the Authentication-Results and AAR headers per Section Section 5.2.1.

9.3. DMARC Reporting of ARC Findings - Interim

[[ Note: Discussion on the IETF DMARC-WG list has indicated some interest in more substantial reporting for analytic purposes. To support that effort, the following guidance is provided only as an interim, minimal data set. A more complete reporting construct will be specified in a related spec - TBD. (see the additional fields specified in Section 5.2.1) ]]

Receivers SHOULD indicate situations in which ARC evaluation influenced the results of their local policy determination. DMARC reporting of ARC-informed decisions can be accomplished by adding a local_policy comment explanation containing the list of data discovered in the ARC evaluation (Section 9.1 and Section 5.2.1):

<policy_evaluated>
  <disposition>delivered</disposition>
  <dkim>fail</dkim>
  <spf>fail <comment>source.ip=10.0.0.1</comment></spf>
  <reason>
   <type>local_policy</type>
   <comment>arc=pass ams[2].d=d2.example ams[2].s=s1 as[2].d=d2.example 
     as[2].s=s2 as[1].d=d1.example as[1].s=s3</comment>
  </reason>
</policy_evaluated>

In the suggested sample, d2.example is the sealing domain for ARC[2] and d1.example is the sealing domain for ARC[1].

Mediators SHOULD generate DMARC reports on messages which transit their system just like any other message which they receive. This will result in multiple reports for each mediated message as they transit the series of handlers. DMARC report consumers should be aware of this behaviour and make the necessary accommodations.

10. Supporting Alternate Signing Algorithms

This section has been moved to [ARC-MULTI]

11. Privacy Considerations

The ARC chain provides a verifiable record of the handlers for a message. Anonymous remailers will probably not find this compatible with their operating goals.

12. IANA Considerations

This specification adds three new header fields as defined below.

12.1. Authentication-Results Method Registry Update

This draft adds one item to the IANA “Email Authentication Methods” registry:

12.2. Definitions of the ARC header fields

This specification adds three new header fields to the “Permanent Message Header Field Registry”, as follows:

13. Security Considerations

The Security Considerations of [RFC6376] and [RFC7601] apply directly to this specification.

13.1. Header Size

Inclusion of ARC sets in the header of emails may cause problems for some older or more constrained MTAs if they are unable to accept the greater size of the header.

13.2. DNS Operations

Operators who receive a message bearing N ARC sets have to complete up to N+1 DNS queries to evaluate the chain (barring DNS redirection mechanisms which can increase the lookups for a given target value). This has at least two effects:

  1. An attacker can send a message to an ARC partipant with a concocted sequence of ARC sets bearing the domains of intended victims, and all of them will be queried by the participant until a failure is discovered. The difficulty of forging the signature values should limit the extent of this load to domains under control of the attacker.
  2. DKIM only does one DNS check per signature, while this one can do many (per chain). Absent caching, slow DNS responses can cause SMTP timeouts; and backlogged delivery queues on mediating systems. This could be exploited as a DoS attack.

13.3. Message Content Suspicion

Recipients are cautioned to treat messages bearing ARC sets with the same suspicion that they apply to all other email messages. This includes appropriate content scanning and other checks for potentially malicious content. The handlers which are identified within the ARC chain may be used to provide input to local policy engines in cases where DMARC validation fails (due to mediation impacting SPF attribution, DKIM validity or alignment).

Note that a passing ARC chain may not adequately mean that the message is safe because:

  1. You have to trust all signatories; and
  2. Even trusted systems may have become compromised or may not properly authenticate messages, so even with a chain of trusted participants, the message might still never have authenticated in the first place (which is why you have the AAR to inspect) or could have been subject to unintended modifications.

14. Evaluating the Efficacy of the ARC Protocol

The ARC protocol is designed to mitigate some of the most common failure conditions for email which transits intermediary handlers en route to the final recipient. Some of these problems have happened due to the adoption of the DMARC protocol [RFC7489] and are listed in [RFC6377] and [RFC7960].

As the ARC protocol becomes standardized and implemented amongst intermediary handlers, the following aspects should be evaluated in order to determine the success of the protocol in accomplishing the intended benefits.

NOTE: Terminology within this section does NOT follow [RFC2119] interpretation. This section represents the current thoughts of the working group regarding unanswered questions related to the protocol. Wider deployment will inform these topics and probably expand them.

14.1. Success Consideration

Currently, many receivers have heuristically determined overrides in order to rescue mail from intermediary-caused failures. Many of those overrides rely on inferrence rather than direct evidence.

ARC will be a success if, for ARC sealed messages, receivers are able to implment ARC-based algorithmic decisions based on the direct evidence found within the ARC chain. This is especially relevant for DMARC processing when the DKIM d= value is aligned with the rfc5322.From author domain.

14.2. Failure Considerations

The intent of ARC is to be at most value-add and at worst benign. If ARC opens up significant new vectors for abuse (see Section 13) then this protocol will be a failure. Note that weaknesses inherent in the mail protocols ARC is built upon (such as DKIM replay attacks and other known issues) are not new vectors which can be attributed to this specification.

14.3. Open Questions

The following open questions are academic and have no clear answer at the time of the development of the protocol. However, wide-spread deployment should be able to gather the necessary data to answer some or all of them.

14.3.1. Value of the ARC-Seal (AS) Header

Data should be collected to show if the ARC-Seal (AS) provides value beyond the ARC Message Signature (AMS) for either making delivery decisions or catching malicious actors trying to craft or replay malicious chains.

14.3.2. DNS Overhead

Longer ARC chains will require more queries to retrieve the keys for validating the chain. While this is not believed to be a security issue (see Section 13.2), it is unclear how much overhead will truly be added. This is similar to some of the initial processing and query load concerns which were debated at the time of the DKIM specification development.

Data should be collected to better understand usable length and distribution of lengths found in valid ARC chains along with the the DNS impact of processing ARC chains.

14.3.3. Distinguishing Valuable from Worthless Trace Information

There are several edge cases where the information in the AAR can make the difference between message delivery or rejection. For example, if there is a well known mailing list that ARC seals but doesn’t do its own initial DMARC enforcement, a Final Receiver with this knowledge could make a delivery decision based upon the authentication information it sees in the corresponding AAR header.

Certain trace information in the AAR is useful/necessary in the construction of DMARC reports. It would be beneficial to identify the value-add of having intermediary-handled mail flow information added into the DMARC reports going back to senders.

Certain receivers believe the entire set of trace information would be valuable to feed into machine learning systems to identify fraud and/or provide other signals related to message delivery.

It is unclear what trace information will be valuable for all receivers, regardless of size.

Data should be collected on what trace information receivers are using that provides useful signals that affect deliverability, and what portions of the trace data are left untouched or provide no useful information.

Since many such systems are intentionly proprietary or confidential to prevent gaming by abusers, it may not be viable to reliably answer this particular question. The evolving nature of attacks can also shift the landscape of “useful” information over time.

15. Implementation Status

[[ Note: For minimizing section number references when the RFC editor removes this section, it has been moved to be the last section of the document before the Appendicies. ]]

[[ Note to the RFC Editor: Please remove this section before publication along with the reference to [RFC6982]. ]]

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC6982]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.

This information is known to be correct as of the seventh interoperability test event which was held on 2017-07-15 & 16 at IETF99.

For a few of the implementations, later status information was available as of December 2017.

15.1. GMail test reflector and incoming validation

Organization: Google

Description: Internal production implementation with both debug analysis and validating + sealing pass-through function

Status of Operation: Production - Incoming Validation

Coverage: Full spec implemented as of [ARC-DRAFT-06]

Licensing: Proprietary - Internal only

Implementation Notes:

Contact Info: arc-discuss@dmarc.org

15.2. AOL test reflector and internal tagging

Organization: AOL

Description: Internal prototype implementation with both debug analysis and validating + sealing pass-through function

Status of Operation: Beta

Coverage: ARC chain validity status checking is operational, but only applied to email addresses enrolled in the test program. This system conforms to [ARC-DRAFT-06]

Licensing: Proprietary - Internal only

Implementation Notes:

Contact Info: arc-discuss@dmarc.org

15.3. dkimpy

Organization: dkimpy developers/Scott Kitterman

Description: Python DKIM package

Status of Operation: Production

Coverage:

Licensing: Open/Other (same as dkimpy package = BCD version 2)

Contact Info: https://launchpad.net/dkimpy

15.4. OpenARC

Organization: TDP/Murray Kucherawy

Description: Implemention of milter functionality related to the OpenDKIM and OpenDMARC packages

Status of Operation: Beta

Coverage: Built to support [ARC-DRAFT-10]

Licensing: Open/Other (same as OpenDKIM and OpenDMARC packages)

Implementation Notes:

Contact Info: arc-discuss@dmarc.org

15.5. Mailman 3.2 patch

Organization: Mailman development team

Description: Integrated ARC capabilities within the Mailman 3.2 package

Status of Operation: Patch submitted

Coverage: Based on OpenARC

Licensing: Same as mailman package - GPL

Implementation Notes:

Contact Info: https://www.gnu.org/software/mailman/contact.html

15.6. Copernica/MailerQ web-based validation

Organization: Copernica

Description: Web-based validation of ARC-signed messages

Status of Operation: Beta

Coverage: Built to support [ARC-DRAFT-05]

Licensing: On-line usage only

Implementation Notes:

Contact Info: https://www.copernica.com/

15.7. Rspamd

Organization: Rspamd community

Description: ARC signing and verification module

Status of Operation: Production, though deployment usage is unknown

Coverage: Built to support [ARC-DRAFT-06]

Licensing: Open source

Implementation Notes:

Contact Info: https://rspamd.com/doc/modules/arc.html and https://github.com/vstakhov/rspamd

15.8. PERL MAIL::DKIM module

Organization: FastMail

Description: Email domain authentication (sign and/or verify) module, previously included SPF / DKIM / DMARC, now has ARC added

Status of Operation: Production, deployment usage unknown

Coverage: Built to support [ARC-DRAFT-10]

Licensing: Open Source

Implementation Notes:

Contact Info: http://search.cpan.org/~mbradshaw/Mail-DKIM-0.50/

15.9. PERL Mail::Milter::Authentication module

Organization: FastMail

Description: Email domain authentication milter, uses MAIL::DKIM (see above)

Status of Operation: Intial validation completed during IETF99 hackathon with some follow-on work during the week

Coverage: Built to support [I-D.ARC]

Licensing: Open Source

Implementation Notes:

Contact Info: https://github.com/fastmail/authentication_milter

15.10. Sympa List Manager

Organization: Sympa Dev Community

Description: Work in progress

Status of Operation: Work in progress

Coverage: unknown

Licensing: open source

Implementation Notes:

Contact Info: https://github.com/sympa-community

15.11. Oracle Messaging Server

Organization: Oracle

Description:

Status of Operation: Intial development work during IETF99 hackathon. Status since then unknown.

Coverage: Built to support [ARC-DRAFT-06]

Licensing: Unknown

Implementation Notes:

Contact Info:

15.12. MessageSystems Momentum

Organization: MessageSystems/SparkPost

Description: OpenARC integration into the LUA-enabled Momentum processing space

Status of Operation: Beta

Coverage: Built to support [ARC-DRAFT-10]

Licensing: Unknown

Implementation Notes:

Contact Info:

16. References

16.1. Normative References

[RFC1345] Simonsen, K., "Character Mnemonics and Character Sets", RFC 1345, DOI 10.17487/RFC1345, June 1992.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2142] Crocker, D., "Mailbox Names for Common Services, Roles and Functions", RFC 2142, DOI 10.17487/RFC2142, May 1997.
[RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS Names", BCP 32, RFC 2606, DOI 10.17487/RFC2606, June 1999.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 3463, DOI 10.17487/RFC3463, January 2003.
[RFC4686] Fenton, J., "Analysis of Threats Motivating DomainKeys Identified Mail (DKIM)", RFC 4686, DOI 10.17487/RFC4686, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008.
[RFC5585] Hansen, T., Crocker, D. and P. Hallam-Baker, "DomainKeys Identified Mail (DKIM) Service Overview", RFC 5585, DOI 10.17487/RFC5585, July 2009.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, DOI 10.17487/RFC5598, July 2009.
[RFC5863] Hansen, T., Siegel, E., Hallam-Baker, P. and D. Crocker, "DomainKeys Identified Mail (DKIM) Development, Deployment, and Operations", RFC 5863, DOI 10.17487/RFC5863, May 2010.
[RFC6376] Crocker, D., Hansen, T. and M. Kucherawy, "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, September 2011.
[RFC6377] Kucherawy, M., "DomainKeys Identified Mail (DKIM) and Mailing Lists", BCP 167, RFC 6377, DOI 10.17487/RFC6377, September 2011.
[RFC6651] Kucherawy, M., "Extensions to DomainKeys Identified Mail (DKIM) for Failure Reporting", RFC 6651, DOI 10.17487/RFC6651, June 2012.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1", RFC 7208, DOI 10.17487/RFC7208, April 2014.
[RFC7601] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 7601, DOI 10.17487/RFC7601, August 2015.

16.2. Informative References

[ARC-DRAFT-05] Andersen, K., "Authenticated Received Chain (ARC) Protocol (I-D-05)", n.d..
[ARC-DRAFT-06] Andersen, K., "Authenticated Received Chain (ARC) Protocol (I-D-06)", n.d..
[ARC-DRAFT-10] Andersen, K., "Authenticated Received Chain (ARC) Protocol (I-D-10)", n.d..
[ARC-MULTI] Andersen, K., "Using Multiple Signing Algorithms with ARC", January 2018.
[ARC-TEST] Blank, S., "ARC Test Suite", January 2017.
[ARC-USAGE] Jones, S., Adams, T., Rae-Grant, J. and K. Andersen, "Recommended Usage of the ARC Headers", December 2017.
[ENHANCED-STATUS] "IANA SMTP Enhanced Status Codes", n.d..
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013.
[RFC7489] Kucherawy, M. and E. Zwicky, "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015.
[RFC7960] Martin, F., Lear, E., Draegen. Ed., T., Zwicky, E. and K. Andersen, "Interoperability Issues between Domain-based Message Authentication, Reporting, and Conformance (DMARC) and Indirect Email Flows", RFC 7960, DOI 10.17487/RFC7960, September 2016.

Appendix A. Appendix A - Design Requirements

(This section is re-inserted for background information from [ARC-DRAFT-06] and earlier versions.)

The specification of the ARC framework is driven by the following high-level goals, security considerations, and practical operational requirements.

A.1. Primary Design Criteria

A.2. Out of Scope

ARC is not a trust framework. Users of the ARC header fields are cautioned against making unsubstantiated conclusions when encountering a “broken” ARC sequence.

Appendix B. Appendix B - Example Usage

[[ Note: The following examples were mocked up early in the definition process for the spec. They no longer reflect the current definition and need various updates which will be included in a future draft. ]]

(Obsolete but retained for illustrative purposes)

B.1. Example 1: Simple mailing list

B.1.1. Here’s the message as it exits the Origin:

Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
     bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
     gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@dmarc.org
Subject: Example 1
 
Hey gang,
This is a test message.
--J.

B.1.2. Message is then received at example.org

B.1.2.1. Example 1, Step A: Message forwarded to list members

Processing at example.org:

Here’s the message as it exits example.org:

Return-Path: <jqd@d1.example>
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1F5
     vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+m4bw
     a6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.1.3. Example 1: Message received by Recipient

Let’s say that the Recipient is example.com

Processing at example.com:

Here’s what the message looks like at this point:

Return-Path: <jqd@d1.example>
Received: from example.org (example.org [208.69.40.157])
    by clothilde.example.com with ESMTP id 
    d200mr22663000ykb.93.1421363207
    for <fmartin@example.com>; Thu, 14 Jan 2015 15:02:40 -0800 (PST)
Authentication-Results: clothilde.example.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
     1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
     A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
     bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
     gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.2. Example 2: Mailing list to forwarded mailbox

B.2.1. Here’s the message as it exits the Origin:

Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
     bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
     gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: Example 1
 
Hey gang,
This is a test message.
--J.

B.2.2. Message is then received at example.org

B.2.2.1. Example 2, Step A: Message forwarded to list members

Processing at example.org:

Here’s the message as it exits Step A:

Return-Path: <jqd@d1.example>
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
     1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
     69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
     1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
     A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.2.2.2. Example 2, Step B: Message from list forwarded

The message is delivered to a mailbox at gmail.com
Processing at gmail.com:

Here’s what the message looks like at this point:

Return-Path: <jqd@d1.example>
ARC-Seal: i=2; a=rsa-sha256; t=1421363253;
    s=notary01; d=gmail.com; cv=pass; 
    b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDWR
     YbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/sut
     txO+RRNr0fCFw==
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
    d=gmail.com; s=20120806;
    h=mime-version:content-type:x-original-sender:
     x-original-authentication-results:precedence:mailing-list:
     list-id:list-post:list-help:list-archive:sender:reply-to:
     list-unsubscribe:DKIM-Signature;
    bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBmfhS
     LF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJRFeM
     KdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwDBJtXw
     bQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
    for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=2; gmail.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=none:
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
     1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
     A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.2.3. Example 2: Message received by Recipient

Let’s say that the Recipient is example.com
Processing at example.com:

Here’s what the message looks like at this point:

Return-Path: <jqd@d1.example>
Received: from mail-ob0-f188.google.com (mail-ob0-f188.google.com
    [208.69.40.157]) by clothilde.example.com with ESMTP id
    d200mr22663000ykb.93.1421363268
    for <fmartin@example.com>; Thu, 14 Jan 2015 15:03:15 -0800 (PST)
Authentication-Results: clothilde.example.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@gmail.com; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363253;
    s=notary01; d=gmail.com; cv=pass; 
    b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDWR
     YbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/sut
     txO+RRNr0fCFw==
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
    d=gmail.com; s=20120806;
    h=mime-version:content-type:x-original-sender:
     x-original-authentication-results:precedence:mailing-list:
     list-id:list-post:list-help:list-archive:sender:reply-to:
     :list-unsubscribe:DKIM-Signature;
    bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBmfhS
     LF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJRFeM
     KdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwDBJtXw
     bQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
    for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=2; gmail.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
     1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
     A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
    s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
     Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.3. Example 3: Mailing list to forwarded mailbox with source

B.3.1. Here’s the message as it exits the Origin:

Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=origin2015; d=d1.example; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61T
     X6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69EU
     8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=d1.example; s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrv
     Qwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3
     TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: Example 1
 
Hey gang,
This is a test message.
--J.

B.3.2. Message is then received at example.org

B.3.2.1. Example 3, Step A: Message forwarded to list members with source

Processing at example.org:

Here’s the message as it exits Step A:

Return-Path: <jqd@d1.example>
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=pass; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
     1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
     69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:From:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
     1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
     A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=origin2015; d=d1.example; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=d1.example; s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.3.2.2. Example 3, Step B: Message from list forwarded with source

The message is delivered to a mailbox at gmail.com
Processing at gmail.com:

Here’s what the message looks like at this point:

Return-Path: <jqd@d1.example>
ARC-Seal: i=3; a=rsa-sha256; t=1421363253;
    s=notary01; d=gmail.com; cv=pass; 
    b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwD
     WRYbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF
     /suttxO+RRNr0fCFw==
ARC-Message-Signature: i=3; a=rsa-sha256; c=relaxed/relaxed;
    d=gmail.com; s=20120806;
    h=mime-version:content-type:x-original-sender
     :x-original-authentication-results:precedence:mailing-list
     :list-id:list-post:list-help:list-archive:sender
     :list-unsubscribe:reply-to;
    bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
     1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
     69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBm
     fhSLF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJ
     RFeMKdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwD
     BJtXwbQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
    for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=3; gmail.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=pass; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1
     F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+
     m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=origin2015; d=d1.example; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=d1.example; s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYij
     rvQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD
     4Gd3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

B.3.3. Example 3: Message received by Recipient

Let’s say that the Recipient is example.com
Processing at example.com:

Here’s what the message looks like at this point:

Return-Path: <jqd@d1.example>
Received: from mail-ob0-f188.google.com (mail-ob0-f188.google.com
    [208.69.40.157]) by clothilde.example.com with ESMTP id
    d200mr22663000ykb.93.1421363268
    for <fmartin@example.com>; Thu, 14 Jan 2015 15:03:15 -0800 (PST)
Authentication-Results: clothilde.example.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@gmail.com; dmarc=fail; arc=pass
ARC-Seal: i=3; a=rsa-sha256; t=1421363253;
    s=notary01; d=gmail.com; cv=pass; 
    b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDW
     RYbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/s
     uttxO+RRNr0fCFw==
ARC-Message-Signature: i=3; a=rsa-sha256; c=relaxed/relaxed;
    d=gmail.com; s=20120806;
    h=mime-version:content-type:x-original-sender
     :x-original-authentication-results:precedence
     :mailing-list:list-id:list-post:list-help:list-archive:sender
     :list-unsubscribe:reply-to;
    bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
     1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
     69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBm
     fhSLF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJ
     RFeMKdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwD
     BJtXwbQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
    for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=3; gmail.com; spf=fail
    smtp.from=jqd@d1.example; dkim=pass (1024-bit key) 
    header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
    s=seal2015; d=example.org; cv=pass; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
     1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
     69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
    d=example.org; s=clochette; t=1421363105;
    bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
    h=List-Id:List-Unsubscribe:List-Archive:List-Post:
     List-Help:List-Subscribe:Reply-To:DKIM-Signature;
    b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1
     F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+
     m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
    by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
    for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
    spf=pass smtp.mfrom=jqd@d1.example;
    dkim=pass (1024-bit key) header.i=@d1.example; 
    dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
    (authenticated bits=0)
    by segv.d1.example with ESMTP id t0FN4a8O084569;
    Thu, 14 Jan 2015 15:00:01 -0800 (PST)
    (envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
    s=origin2015; d=d1.example; cv=none; 
    b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
     TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
     EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
    d=d1.example; s=20130426; t=1421363082;
    bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
    h=MIME-Version:To:CC:Subject:Content-Type:Content-Transfer-Encoding;
    b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
     vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
     d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
 
Hey gang,
This is a test message.
--J.

Appendix C. Acknowledgements

This draft is the work of OAR-Dev Group.

The authors thank all of the OAR-Dev group for the ongoing help and though-provoking discussions from all the participants, especially: Alex Brotman, Brandon Long, Dave Crocker, Elizabeth Zwicky, Franck Martin, Greg Colburn, J. Trent Adams, John Rae-Grant, Mike Hammer, Mike Jones, Steve Jones, Terry Zink, Tim Draegen.

Grateful appreciation is extended to the people who provided feedback through the discuss mailing list.

Appendix D. Comments and Feedback

Please address all comments, discussions, and questions to dmarc@ietf.org. Earlier discussions can be found at arc-discuss@dmarc.org.

Authors' Addresses

Kurt Andersen LinkedIn 1000 West Maude Ave Sunnyvale, California 94085 USA EMail: kurta@linkedin.com
Brandon Long (editor) Google EMail: blong@google.com
Steven Jones (editor) TDP EMail: smj@crash.com
Seth Blank (editor) ValiMail EMail: seth@valimail.com
Murray Kucherawy (editor) TDP EMail: superuser@gmail.com