DMARC A. Brotman (ed) Internet-Draft Comcast, Inc. Obsoletes: 7489 (if approved) 20 November 2024 Intended status: Standards Track Expires: 24 May 2025 Domain-based Message Authentication, Reporting, and Conformance (DMARC) Aggregate Reporting draft-ietf-dmarc-aggregate-reporting-22 Abstract Domain-based Message Authentication, Reporting, and Conformance (DMARC) allows for Domain Owners to request aggregate reports from receivers. This report is an XML document, and contains extensible elements that allow for other types of data to be specified later. The aggregate reports can be submitted to the Domain Owner's specified destination as supported by the receiver. 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 24 May 2025. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. Brotman (ed) Expires 24 May 2025 [Page 1] Internet-Draft DMARC Aggregate Reporting November 2024 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. DMARC Feedback . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Aggregate Reports . . . . . . . . . . . . . . . . . . . . 3 2.1.1. Handling Domains in Reports . . . . . . . . . . . . . 6 2.1.2. DKIM Signatures in Aggregate Reports . . . . . . . . 6 2.1.3. Unique Identifiers in Aggregate Reporting . . . . . . 7 2.1.4. Error field . . . . . . . . . . . . . . . . . . . . . 7 2.1.5. Policy Override Reason . . . . . . . . . . . . . . . 7 2.2. Extensions . . . . . . . . . . . . . . . . . . . . . . . 8 2.3. Changes in Policy During Reporting Period . . . . . . . . 8 2.4. Recommended Reporting Periods . . . . . . . . . . . . . . 8 2.5. Report Request Discovery . . . . . . . . . . . . . . . . 9 2.6. Transport . . . . . . . . . . . . . . . . . . . . . . . . 9 2.6.1. Definition of Report-ID . . . . . . . . . . . . . . . 9 2.6.2. Email . . . . . . . . . . . . . . . . . . . . . . . . 9 2.6.3. Other Methods . . . . . . . . . . . . . . . . . . . . 12 2.6.4. Handling of Duplicates . . . . . . . . . . . . . . . 12 3. Verifying External Destinations . . . . . . . . . . . . . . . 12 4. Extensible Reporting . . . . . . . . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 5.1. Registration request for the DMARC namespace: . . . . . . 16 5.2. Registration request for the DMARC XML schema: . . . . . 16 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16 6.1. Report Recipients . . . . . . . . . . . . . . . . . . . . 16 6.2. Data Contained Within Reports . . . . . . . . . . . . . . 17 6.3. Feedback Leakage . . . . . . . . . . . . . . . . . . . . 17 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. Normative References . . . . . . . . . . . . . . . . . . . . 18 9. Informative References . . . . . . . . . . . . . . . . . . . 20 Appendix A. DMARC XML Schema . . . . . . . . . . . . . . . . . . 20 Appendix B. Sample Report . . . . . . . . . . . . . . . . . . . 27 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 29 Brotman (ed) Expires 24 May 2025 [Page 2] Internet-Draft DMARC Aggregate Reporting November 2024 1. Introduction A key component of DMARC [I-D.ietf-dmarc-dmarcbis] is the ability for Domain Owners to request that receivers provide various types of reports. These reports allow Domain Owners to have insight into which IP addresses are sending on their behalf, and some insight into whether or not the volume may be legitimate. These reports expose information relating to the DMARC policy, as well as the outcome of SPF [RFC7208] & DKIM [RFC6376] validation. There are a number of terms defined in [I-D.ietf-dmarc-dmarcbis] that are used within this document. Understanding those definitions will aid in reading this document. 1.1. Terminology 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. 2. DMARC Feedback Providing Domain Owners with visibility into how Mail Receivers implement and enforce the DMARC mechanism in the form of feedback is critical to establishing and maintaining accurate authentication deployments. When Domain Owners can see what effect their policies and practices are having, they are better willing and able to use quarantine and reject policies. 2.1. Aggregate Reports The DMARC aggregate feedback report is designed to provide Domain Owners with precise insight into: * authentication results, * corrective action that needs to be taken by Domain Owners, and * the effect of Domain Owner DMARC policy on email streams processed by Mail Receivers. Brotman (ed) Expires 24 May 2025 [Page 3] Internet-Draft DMARC Aggregate Reporting November 2024 Aggregate DMARC feedback provides visibility into real-world email streams that Domain Owners need in order to make informed decisions regarding the publication of DMARC policy. When Domain Owners know what legitimate mail they are sending, what the authentication results are on that mail, and what forged mail receivers are getting, they can make better decisions about the policies they need and the steps they need to take to enable those policies. When Domain Owners set policies appropriately and understand their effects, Mail Receivers can act on them confidently. Visibility comes in the form of daily (or more frequent) Mail Receiver-originated feedback reports that contain aggregate data on message streams relevant to the Domain Owner. This information includes data about messages that passed DMARC authentication as well as those that did not. A separate report MUST be generated for each Policy Domain encountered during the reporting period. See below for further explanation in "Handling Domains in Reports". The report may include the following data: * The DMARC policy discovered and applied, if any * The selected message disposition * The identifier evaluated by SPF and the SPF result, if any * The identifier evaluated by DKIM and the DKIM result, if any * For both DKIM and SPF, an indication of whether the identifier was in DMARC alignment (see [I-D.ietf-dmarc-dmarcbis], Section 3.2.7) * Sending and receiving domains * The number of successful authentications * The counts of messages based on all messages received, even if their delivery is ultimately blocked by other filtering agents. The format for these reports is defined in Appendix A. DMARC Aggregate Reports MUST contain two primary sections ("metadata" & "data" below) ; one consisting of descriptive information (with two elements), and the other a set of IP address-focused row-based data. Each report MUST contain data for only one Policy Domain. A single report MUST contain data for one policy configuration. If multiple configurations were observed during a single reporting period, a reporting entity MAY choose to send multiple reports, otherwise the reporting entity SHOULD note only the final configuration observed during the period. See below for further information. The informative section MUST contain two elements. One will be the metadata section which MUST contain the fields related to "org_name", "email", "report_id", and "date_range". Optional fields MAY include Brotman (ed) Expires 24 May 2025 [Page 4] Internet-Draft DMARC Aggregate Reporting November 2024 "extra_contact_info", an "error" field. The "date_range" field will contain "begin" and "end" fields as epoch timestamps. The other element will be the "policy_published", which will record the policy configuration observed by the receiving system. Mandatory fields are "domain", "p", "sp". Optional fields are "fo", "adkim", "aspf", "testing", and "discovery_method". There MAY be an optional third section, "extension". Within the data section, the report will contain record(s) stating which IP addresses were seen to have delivered messages for the Author Domain to the receiving system. For each IP address that is being reported, there will be at least one "record" element. Each "record" element will have one "row", one "identifiers", and one "auth_results" sub-element. Within the "row" element, there MUST be "source_ip" and "count". There MUST also exist a "policy_evaluated", with sub-elements of "disposition", "dkim", and "spf". There MAY be an element for "reason", meant to include any notes the reporter might want to include as to why the "disposition" policy does not match the "policy_published", such as a Local Policy override (See Section 2.1.5, Policy Override Reason). The "dkim" and "spf" elements MUST be the evaluated values as they relate to DMARC, not the values the receiver may have used when overriding the policy. Within the "identifiers" element, there MUST exist the data that was used to apply policy for the given IP address. There MUST be a "header_from" element, which will contain the RFC5322.From domain from the message. There MAY be an optional "envelope_from" element, which contains the RFC5321.MailFrom domain that the SPF check has been applied to. This element MAY be existing but empty if the message had a null reverse-path ([RFC5321], Section 4.5.5). There MAY be an optional "envelope_to" element, which contains the RFC5321.RcptTo (see [RFC5598]) domain from the message. There MUST be an "auth_results" element within the "record" element. This will contain the data related to authenticating the messages associated with this sending IP address. There MAY be a number of optional "dkim" sub-elements, one for each checked DKIM signature. There MAY be an optoinal "spf" sub-element. These elements MUST have a "domain" that was used during validation, as well as "result". If validation is attempted for any DKIM signature, the results MUST be included in the report (within reason, see "DKIM Signatures in Aggregate Reports" below for handling numerous signatures). The "dkim" element MUST include a "selector" element that was observed during validation. For the "spf" element, the "result" element MUST contain a lower-case string where the value is one of the results defined in [RFC8601] Section 2.7.2. The "dkim" result MUST contain a lower-case string where the value is one of the results defined in [RFC8601] Section 2.7.1. Both the "spf" and "dkim" results may optionally include a "human_readable" field meant Brotman (ed) Expires 24 May 2025 [Page 5] Internet-Draft DMARC Aggregate Reporting November 2024 for the report to convey more descriptive information back to the Domain Owner relating to evaluation failures. There MAY exist an optional section for extensions. 2.1.1. Handling Domains in Reports In the same report, there MUST be a single Policy Domain, though there could be multiple RFC5322.From Domains. Each RFC5322.From domain will create its own "record" within the report. Consider the case where there are three domains with traffic volume to report: example.com, foo.example.com, and bar.example.com. There will be explicit DMARC records for example.com and bar.example.com, with distinct policies. There is no explicit DMARC record for foo.example.com, so it will be reliant on the policy described for example.com. For a report period, there would now be two reports. The first will be for bar.example.com, and contain only one "record", for bar.example.com. The second report would be for example domain contain multiple "record" elements, one for example.com and one for foo.example.com (and extensibly, other "record" elements for subdomains which likewise did not have an explicit DMARC policy declared). 2.1.2. DKIM Signatures in Aggregate Reports Within a single message, the possibility exists that there could be multiple DKIM signatures. When validation of the message occurs, some signatures may pass, while some may not. As these pertain to DMARC, and especially to aggregate reporting, reporters may not find it clear which DKIM signatures they should include in a report. Signatures, regardless of outcome, could help the report ingester determine the source of a message. However, there is a preference as to which signatures are included. 1. A signature that passes DKIM, in strict alignment with the RFC5322.From domain 2. A signature that passes DKIM, in relaxed alignment with the RFC5322.From domain 3. Any other DKIM signatures that pass 4. DKIM signatures that do not pass A report SHOULD contain no more than 100 signatures for a given "row", in decreasing priority. Brotman (ed) Expires 24 May 2025 [Page 6] Internet-Draft DMARC Aggregate Reporting November 2024 2.1.3. Unique Identifiers in Aggregate Reporting There are a few places where a unique identifier is specified as part of the body of the report, the subject, and so on. These unique identifiers should be consistent per each report. Specified below, the reader will see a "Report-ID" and "unique-id". These are the fields that MUST be identical when used. 2.1.4. Error field A few examples of information contained within the error field(s): * DMARC DNS record evaluation errors (invalid rua or sp, etc.) * Multiple DMARC records at a given location Be mindful that the error field is an unbounded string, but should not contain an extremely large body. Provide enough information to assist the domain owner with understanding some issues with their authentication or DMARC declaration. 2.1.5. Policy Override Reason The reason element, indicating an override of the DMARC policy, consists of a mandatory type field and an optional comment field. The type field MUST have one of the pre-defined values listed below. The comment field is an unbounded string for providing further details. Possible values for the policy override type: "local_policy": The Mail Receiver's local policy exempted the message from being subjected to the Domain Owner's requested policy action. "mailing_list": Local heuristics determined that the message arrived via a mailing list, and thus authentication of the original message was not expected to succeed. "other": Some policy exception not covered by the other entries in this list occurred. Additional detail can be found in the PolicyOverrideReason's "comment" field. "policy_test_mode": The message was exempted from application of policy by the testing mode ("t" tag) in the DMARC policy record. "trusted_forwarder": Message authentication failure was anticipated by other evidence linking the message to a locally maintained list of known and trusted forwarders. Brotman (ed) Expires 24 May 2025 [Page 7] Internet-Draft DMARC Aggregate Reporting November 2024 2.2. Extensions There MAY be optional sections for extensions within the document. The absence or existence of this section SHOULD NOT create an error when processing reports. This will be covered in a separate section. 2.3. Changes in Policy During Reporting Period Note that Domain Owners or their agents may change the published DMARC policy for a domain or subdomain at any time. From a Mail Receiver's perspective, this will occur during a reporting period and may be noticed during that period, at the end of that period when reports are generated, or during a subsequent reporting period, all depending on the Mail Receiver's implementation. Under these conditions, it is possible that a Mail Receiver could do any of the following: * generate for such a reporting period a single aggregate report that includes message dispositions based on the old policy, or a mix of the two policies, even though the report only contains a single "policy_published" element; * generate multiple reports for the same period, one for each published policy occurring during the reporting period; Such policy changes are expected to be infrequent for any given domain, whereas more stringent policy monitoring requirements on the Mail Receiver would produce a very large burden at Internet scale. Therefore, it is the responsibility of report consumers (i.e., vendors) and Domain Owners to be aware of this situation and expect such mixed reports during the propagation of the new policy to Mail Receivers. 2.4. Recommended Reporting Periods Aggregate reports are most useful when they all cover a common time period. By contrast, correlation of these reports from multiple generators when they cover incongruent time periods is difficult or impossible. Report generators should, wherever possible, adhere to hour boundaries for the reporting period they are using. For example, starting a per-day report at 00:00; starting per-hour reports at 00:00, 01:00, 02:00; etc. Report generators using a 24-hour report period are strongly encouraged to begin that period at 00:00 UTC, regardless of local timezone or time of report production, in order to facilitate correlation. Brotman (ed) Expires 24 May 2025 [Page 8] Internet-Draft DMARC Aggregate Reporting November 2024 2.5. Report Request Discovery A Mail Receiver discovers reporting requests when it looks up a DMARC policy record that corresponds to an RFC5322.From domain on received mail. The presence of the "rua" tag specifies where to send feedback. 2.6. Transport The Mail Receiver, after preparing a report, MUST evaluate the provided reporting URIs (See [I-D.ietf-dmarc-dmarcbis]) in the order given. Any reporting URI that includes a size limitation exceeded by the generated report (after compression and after any encoding required by the particular transport mechanism) MUST NOT be used. An attempt MUST be made to deliver an aggregate report to every remaining URI, up to the Receiver's limits on supported URIs. If transport is not possible because the services advertised by the published URIs are not able to accept reports (e.g., the URI refers to a service that is unreachable, or all provided URIs specify size limits exceeded by the generated record), the Mail Receiver MAY send a short report indicating that a report is available but could not be sent. The Mail Receiver MAY cache that data and try again later, or MAY discard data that could not be sent. Where the URI specified in a "rua" tag does not specify otherwise, a Mail Receiver generating a feedback report SHOULD employ a secure transport mechanism. 2.6.1. Definition of Report-ID This identifier MUST be unique among reports to the same domain to aid receivers in identifying duplicate reports should they happen. ridfmt = (dot-atom-text ["@" dot-atom-text]) ; from RFC5322 ridtxt = ("<" ridfmt ">") / ridfmt The format specified here is not very strict as the key goal is uniqueness. 2.6.2. Email The message generated by the Mail Receiver MUST be a [RFC5322] message formatted per [RFC2045]. The aggregate report itself MUST be included in one of the parts of the message. A human-readable annotation MAY be included as a body part (with a human-friendly content-type, such as "text/plain" or "text/html"). Brotman (ed) Expires 24 May 2025 [Page 9] Internet-Draft DMARC Aggregate Reporting November 2024 The aggregate data MUST be an XML file that SHOULD be subjected to GZIP [RFC1952] compression. Declining to apply compression can cause the report to be too large for a receiver to process (the total message size could exceed the receiver SMTP size limit); doing the compression increases the chances of acceptance of the report at some compute cost. The aggregate data MUST be present using the media type "application/gzip" if compressed (see [RFC6713]), and "text/xml" otherwise. The filename MUST be constructed using the following ABNF: filename = receiver "!" policy-domain "!" begin-timestamp "!" end-timestamp [ "!" unique-id ] "." extension receiver = domain ; imported from [@!RFC5322] policy-domain = domain begin-timestamp = 1*DIGIT ; seconds since 00:00:00 UTC January 1, 1970 ; indicating start of the time range contained ; in the report end-timestamp = 1*DIGIT ; seconds since 00:00:00 UTC January 1, 1970 ; indicating end of the time range contained ; in the report unique-id = 1*(ALPHA / DIGIT) extension = "xml" / "xml.gz" The extension MUST be "xml" for a plain XML file, or "xml.gz" for an XML file compressed using GZIP. "unique-id" allows an optional unique ID generated by the Mail Receiver to distinguish among multiple reports generated simultaneously by different sources within the same Domain Owner. A viable option may be to explore UUIDs [RFC9562]. If a report generator needs to re-send a report, the system MUST use the same filename as the original report. This would allow the receiver to overwrite the data from the original, or discard second instance of the report. For example, this is a sample filename for the gzip file of a report to the Domain Owner "example.com" from the Mail Receiver "mail.receiver.example": Brotman (ed) Expires 24 May 2025 [Page 10] Internet-Draft DMARC Aggregate Reporting November 2024 mail.receiver.example!example.com!1013662812!1013749130.xml.gz No specific MIME message structure is required. It is presumed that the aggregate reporting address will be equipped to extract body parts with the prescribed media type and filename and ignore the rest. Email streams carrying DMARC feedback data MUST conform to the DMARC mechanism, thereby resulting in an aligned "pass" (see Section 3.1). This practice minimizes the risk of report consumers processing fraudulent reports. The RFC5322.Subject field for individual report submissions MUST conform to the following ABNF: dmarc-subject = %s"Report" 1*FWS %s"Domain:" 1*FWS domain-name 1*FWS ; policy domain %s"Submitter:" 1*FWS domain-name 1*FWS ; report generator [ %s"Report-ID:" 1*FWS ridtxt ] ; defined below The first domain-name indicates the DNS domain name about which the report was generated. The second domain-name indicates the DNS domain name representing the Mail Receiver generating the report. The purpose of the Report-ID: portion of the field is to enable the Domain Owner to identify and ignore duplicate reports that might be sent by a Mail Receiver. For instance, this is a possible Subject field for a report to the Domain Owner "example.com" from the Mail Receiver "mail.receiver.example". It is folded as allowed by [RFC5322]: Subject: Report Domain: example.com Submitter: mail.receiver.example Report-ID: This transport mechanism potentially encounters a problem when feedback data size exceeds maximum allowable attachment sizes for either the generator or the consumer. Optionally, the report sender MAY choose to use the same "ridtxt" as a part or whole of the RFC5322.Message-Id header included with the report. Doing so may help receivers distinguish when a message is a re-transmission or duplicate report. Brotman (ed) Expires 24 May 2025 [Page 11] Internet-Draft DMARC Aggregate Reporting November 2024 2.6.3. Other Methods The specification as written allows for the addition of other registered URI schemes to be supported in later versions. 2.6.4. Handling of Duplicates There may be a situation where the report generator attempts to deliver duplicate information to the receiver. This may manifest as an exact duplicate of the report, or as duplicate information between two reports. In these situations, the decision of how to handle the duplicate data lies with the receiver. As noted above, the sender MUST use the same unique identifiers when sending the report. This allows the receiver to better understand when duplicates happen. A few options on how to handle that duplicate information: * Reject back to sender, ideally with a permfail error noting the duplicate receipt * Discard upon receipt * Inspect the contents to evaluate the timestamps and reported data, act as appropriate * Accept the duplicate data When accepting the data, that's likely in a situation where it's not yet noticed, or a one-off experience. Long term, duplicate data is not ideal. In the situation of a partial time frame overlap, there is no clear way to distinguish the impact of the overlap. The receiver would need to accept or reject the duplicate data in whole. 3. Verifying External Destinations It is possible to specify destinations for the different reports that are outside the authority of the Domain Owner making the request. This allows domains that do not operate mail servers to request reports and have them go someplace that is able to receive and process them. Without checks, this would allow a bad actor to publish a DMARC policy record that requests that reports be sent to a victim address, and then send a large volume of mail that will fail both DKIM and SPF checks to a wide variety of destinations; the victim will in turn be flooded with unwanted reports. Therefore, a verification mechanism is included. Brotman (ed) Expires 24 May 2025 [Page 12] Internet-Draft DMARC Aggregate Reporting November 2024 When a Mail Receiver discovers a DMARC policy in the DNS, and the Organizational Domain at which that record was discovered is not identical to the Organizational Domain of the host part of the authority component of a [RFC3986] specified in the "rua" tag, the following verification steps MUST be taken: 1. Extract the host portion of the authority component of the URI. Call this the "destination host", as it refers to a Report Receiver. 2. Prepend the string "_report._dmarc". 3. Prepend the domain name from which the policy was retrieved, after conversion to an A-label [RFC5890] if needed. 4. Query the DNS for a TXT record at the constructed name. If the result of this request is a temporary DNS error of some kind (e.g., a timeout), the Mail Receiver MAY elect to temporarily fail the delivery so the verification test can be repeated later. 5. For each record returned, parse the result as a series of "tag=value" pairs, i.e., the same overall format as the policy record (see Section 5.4 in [I-D.ietf-dmarc-dmarcbis]). In particular, the "v=DMARC1" tag is mandatory and MUST appear first in the list. Discard any that do not pass this test. A trailing ";" is optional. 6. If the result includes no TXT resource records that pass basic parsing, a positive determination of the external reporting relationship cannot be made; stop. 7. If at least one TXT resource record remains in the set after parsing, then the external reporting arrangement was authorized by the Report Receiver. 8. If a "rua" tag is thus discovered, replace the corresponding value extracted from the domain's DMARC policy record with the one found in this record. This permits the Report Receiver to override the report destination. However, to prevent loops or indirect abuse, the overriding URI MUST use the same destination host from the first step. For example, if a DMARC policy query for "blue.example.com" contained "rua=mailto:reports@red.example.net" (mailto:reports@red.example.net"), the Organizational Domain host extracted from the latter ("red.example.net") does not match "blue.example.com", so this procedure is enacted. A TXT query for "blue.example.com._report._dmarc.red.example.net" is issued. If a Brotman (ed) Expires 24 May 2025 [Page 13] Internet-Draft DMARC Aggregate Reporting November 2024 single reply comes back containing a tag of "v=DMARC1", then the relationship between the two is confirmed. Moreover, "red.example.net" has the opportunity to override the report destination requested by "blue.example.com" if needed. Where the above algorithm fails to confirm that the external reporting was authorized by the Report Receiver, the URI MUST be ignored by the Mail Receiver generating the report. Further, if the confirming record includes a URI whose host is again different than the domain publishing that override, the Mail Receiver generating the report MUST NOT generate a report to either the original or the override URI. A Report Receiver publishes such a record in its DNS if it wishes to receive reports for other domains. A Report Receiver that is willing to receive reports for any domain can use a wildcard DNS record. For example, a TXT resource record at "*._report._dmarc.example.com" containing at least "v=DMARC1" confirms that example.com is willing to receive DMARC reports for any domain. If the Report Receiver is overcome by volume, it can simply remove the confirming DNS record. However, due to positive caching, the change could take as long as the time-to-live (TTL) on the record to go into effect. 4. Extensible Reporting DMARC reports allow for some extensibility, as defined by future documents that utilize DMARC as a foundation. These extensions MUST be properly formatted XML and meant to exist within the structure of a DMARC report. Two positions of type "" are provided in the existing DMARC structure, one at file level, in an "" element after "" and one at record level, after "". In either case, the extensions MUST contain a URI to the definition of the extension so that the receiver understands how to interpret the data. At file level: Brotman (ed) Expires 24 May 2025 [Page 14] Internet-Draft DMARC Aggregate Reporting November 2024 ... example.com

quarantine

none n never Within the "record" element: ... ... ... ... ... Here "arc-override" and "arc-results" are hypothetical element names defined in the extension's name space. Extension elements are optional. Any number of extensions is allowed. If a processor is unable to handle an extension in a report, it SHOULD ignore the data and continue to the next extension. 5. IANA Considerations This document uses URNs to describe XML namespaces and XML schemas conforming to a registry mechanism described in [RFC3688]. Two URI assignments will be registered by the IANA. Brotman (ed) Expires 24 May 2025 [Page 15] Internet-Draft DMARC Aggregate Reporting November 2024 5.1. Registration request for the DMARC namespace: URI: urn:ietf:params:xml:ns:dmarc-2.0 Registrant Contact: See the "Author's Address" section of this document. XML: None. Namespace URIs do not represent an XML specification. 5.2. Registration request for the DMARC XML schema: URI: urn:ietf:params:xml:schema:dmarc-2.0 Registrant Contact: See the "Author's Address" section of this document. XML: See Appendix A. DMARC XML Schema in this document. 6. Privacy Considerations This section will discuss exposure related to DMARC aggregate reporting. 6.1. Report Recipients A DMARC record can specify that reports should be sent to an intermediary operating on behalf of the Domain Owner. This is done when the Domain Owner contracts with an entity to monitor mail streams for abuse and performance issues. Receipt by third parties of such data may or may not be permitted by the Mail Receiver's privacy policy, terms of use, or other similar governing document. Domain Owners and Mail Receivers should both review and understand if their own internal policies constrain the use and transmission of DMARC reporting. Some potential exists for report recipients to perform traffic analysis, making it possible to obtain metadata about the Receiver's traffic. In addition to verifying compliance with policies, Receivers need to consider that before sending reports to a third party. Brotman (ed) Expires 24 May 2025 [Page 16] Internet-Draft DMARC Aggregate Reporting November 2024 6.2. Data Contained Within Reports Aggregate feedback reports contain aggregated data relating to messages purportedly originating from the Domain Owner. The data does not contain any identifying characteristics about individual users. No personal information such as individual email addresses, IP addresses of individuals, or the content of any messages, is included in reports. Mail Receivers should have no concerns in sending reports as they do not contain personal information. In all cases, the data within the reports relates to the domain-level authentication information provided by mail servers sending messages on behalf of the Domain Owner. This information is necessary to assist Domain Owners in implementing and maintaining DMARC. Domain Owners should have no concerns in receiving reports as they do not contain personal information. The reports only contain aggregated data related to the domain-level authentication details of messages claiming to originate from their domain. This information is essential for the proper implementation and operation of DMARC. Domain Owners who are unable to receive reports for organizational reasons, can choose to exclusively direct the reports to an external processor. 6.3. Feedback Leakage Providing feedback reporting to PSOs for a PSD [RFC9091] can, in some cases, cause information to leak out of an organization to the PSO. This leakage could potentially be utilized as part of a program of pervasive surveillance (see [RFC7624]]). There are roughly three cases to consider: Single Organization PSDs (e.g., ".mil"): RUA reports based on PSD DMARC have the potential to contain information about emails related to entities managed by the organization. Since both the PSO and the Organizational Domain Owners are common, there is no additional privacy risk for either normal or non-existent domain reporting due to PSD DMARC. Multi-organization PSDs that require DMARC usage (e.g., ".bank"): Reports based on PSD DMARC will only be generated for domains that do not publish a DMARC policy at the organizational or host level. For domains that do publish the required DMARC policy records, the feedback reporting addresses of the organization (or hosts) will be used. The only direct risk of feedback leakage for these PSDs are for Organizational Domains that are out of compliance with PSD policy. Data on non-existent cousin domains would be sent to the PSO. Brotman (ed) Expires 24 May 2025 [Page 17] Internet-Draft DMARC Aggregate Reporting November 2024 Multi-organization PSDs (e.g., ".com") that do not mandate DMARC usage: Privacy risks for Organizational Domains that have not deployed DMARC within such PSDs can be significant. For non-DMARC Organizational Domains, all DMARC feedback will be directed to the PSO if that PSO itself has a DMARC record that specifies an RUA. Any non-DMARC Organizational Domain would have its Feedback Reports redirected to the PSO. The content of such reports, particularly for existing domains, is privacy sensitive. PSOs will receive feedback on non-existent domains, which may be similar to existing Organizational Domains. Feedback related to such cousin domains have a small risk of carrying information related to an actual Organizational Domain. To minimize this potential concern, PSD DMARC feedback MUST be limited to Aggregate Reports. Failure Reports carry more detailed information and present a greater risk. 7. Security Considerations * Aggregate reports are supposed to be processed automatically. An attacker might attempt to compromise the integrity or availability of the report processor by sending ill-formed reports. In particular, the archive decompressor and XML parser are at risk to resource exhaustion attacks (zip bomb or XML bomb). * The data contained within aggregate reports may be forged. An attacker might attempt to interfere by submitting false reports in masses. * See also the security considerations of dmarc-bis (Section 11) of [I-D.ietf-dmarc-dmarcbis]. 8. Normative References [I-D.ietf-dmarc-dmarcbis] Herr, T. and J. R. Levine, "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", Work in Progress, Internet-Draft, draft-ietf-dmarc-dmarcbis-36, 20 November 2024, . [RFC1952] Deutsch, P., "GZIP file format specification version 4.3", RFC 1952, DOI 10.17487/RFC1952, May 1996, . [RFC2045] 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, . Brotman (ed) Expires 24 May 2025 [Page 18] Internet-Draft DMARC Aggregate Reporting November 2024 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008, . [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008, . [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, DOI 10.17487/RFC5598, July 2009, . [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, . [RFC6376] 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, . [RFC6713] Levine, J., "The 'application/zlib' and 'application/gzip' Media Types", RFC 6713, DOI 10.17487/RFC6713, August 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, . Brotman (ed) Expires 24 May 2025 [Page 19] Internet-Draft DMARC Aggregate Reporting November 2024 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8601] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 8601, DOI 10.17487/RFC8601, May 2019, . 9. Informative References [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., Trammell, B., Huitema, C., and D. Borkmann, "Confidentiality in the Face of Pervasive Surveillance: A Threat Model and Problem Statement", RFC 7624, DOI 10.17487/RFC7624, August 2015, . [RFC9091] Kitterman, S. and T. Wicinski, Ed., "Experimental Domain- Based Message Authentication, Reporting, and Conformance (DMARC) Extension for Public Suffix Domains", RFC 9091, DOI 10.17487/RFC9091, July 2021, . [RFC9562] Davis, K., Peabody, B., and P. Leach, "Universally Unique IDentifiers (UUIDs)", RFC 9562, DOI 10.17487/RFC9562, May 2024, . Appendix A. DMARC XML Schema Brotman (ed) Expires 24 May 2025 [Page 20] Internet-Draft DMARC Aggregate Reporting November 2024 Brotman (ed) Expires 24 May 2025 [Page 21] Internet-Draft DMARC Aggregate Reporting November 2024 Brotman (ed) Expires 24 May 2025 [Page 22] Internet-Draft DMARC Aggregate Reporting November 2024 Brotman (ed) Expires 24 May 2025 [Page 24] Internet-Draft DMARC Aggregate Reporting November 2024 Brotman (ed) Expires 24 May 2025 [Page 25] Internet-Draft DMARC Aggregate Reporting November 2024 Brotman (ed) Expires 24 May 2025 [Page 26] Internet-Draft DMARC Aggregate Reporting November 2024 Appendix B. Sample Report Brotman (ed) Expires 24 May 2025 [Page 27] Internet-Draft DMARC Aggregate Reporting November 2024 1.0 Sample Reporter report_sender@example-reporter.com ... 3v98abbp8ya9n3va8yr8oa3ya 161212415 161221511 example.com

quarantine

none n treewalk 192.168.4.4 123 pass pass fail example.com example.com example.com pass abc123 example.com fail Acknowledgements Brotman (ed) Expires 24 May 2025 [Page 28] Internet-Draft DMARC Aggregate Reporting November 2024 Many thanks are deserved to those that helped create this document. Much of the content was created from the original [RFC7489], and has now been updated to be more clear and correct some outstanding issues. The IETF DMARC Working Group has spent much time working to finalize this effort, and significant contributions were made by Seth Blank, Todd Herr, Murray S. Kucherawy, Barry Leiba, John Levine, Scott Kitterman, Daniel Kvå (U+00E5)l, Martijn van der Lee, Alessandro Veseley, and Matthä (U+00E4)us Wander. Author's Address Alex Brotman Comcast, Inc. Email: alex_brotman@comcast.com Brotman (ed) Expires 24 May 2025 [Page 29]