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How do DMARC policies and RUA/RUF settings inherit or override each other between a domain and its subdomains?

Summary

Understanding how DMARC policies and RUA/RUF settings interact between parent domains and their subdomains is crucial for effective email authentication. While DMARC policies generally propagate down to subdomains by default, explicit records at the subdomain level can override this inheritance, providing granular control over how different parts of your domain infrastructure handle email authentication failures and report generation. This flexibility allows organizations to tailor their DMARC implementation to specific sending needs, such as using different policies or report destinations for marketing versus transactional email subdomains.

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What email marketers say

Email marketers often face practical challenges when implementing DMARC across complex domain structures, particularly involving subdomains and third-party sending services. There's a common initial confusion regarding whether subdomains automatically inherit policies or require explicit configuration. Many marketers encounter requests from their Email Service Providers (ESPs) to add RUA addresses, raising questions about data sharing and the scope of these reports. Balancing the need for robust email authentication with the complexities of managing multiple sending sources is a recurring theme.

Marketer view

Marketer from Email Geeks notes a client's unusual request to add an RUA for their email marketing tool (Kajabi) to their DMARC record. This is a first encounter with a third party insisting on receiving customer domain RUA reports, leading to questions about the implications. While the information is likely benign, concerns exist that it will include more than just Kajabi emails, prompting a cautious approach.

17 Jan 2024 - Email Geeks

Marketer view

Marketer from Email Geeks finds the RUA request strange, suggesting that the provided RUA addresses might just be examples of what to add. They speculate that it's theoretically possible to add multiple mailto options in a subdomain policy, allowing both DMARC tools and ESPs to receive copies of the reports. This highlights the flexibility, but also the potential for complexity, in DMARC reporting.

17 Jan 2024 - Email Geeks

What the experts say

Email deliverability experts highlight the nuances of DMARC policy application, particularly concerning domain and subdomain interactions. They underscore that while subdomains without explicit DMARC records will inherit the parent's policy, any DMARC record set on a subdomain will take precedence, functioning independently. This independent behavior extends to RUA/RUF reporting, meaning separate reporting destinations can be configured for subdomains, or reports for those subdomains might be missed by the parent's RUA if not explicitly added. Their advice centers on strategic configuration to maintain both security and deliverability.

Expert view

Expert from Email Geeks clarifies that a policy appearing on the subdomain will override the organizational domain policy. This means that once a DMARC record is explicitly set for a subdomain, its directives take precedence over any inherited rules, providing independent control over how that specific subdomain handles email authentication failures.

18 Jan 2024 - Email Geeks

Expert view

Expert from Email Geeks confirms that subdomains without an explicit DMARC policy will indeed inherit it from the organizational domain. This default behavior ensures that even subdomains not specifically configured for DMARC will still be covered by the parent domain's authentication policy, maintaining a baseline level of protection across the entire domain space.

18 Jan 2024 - Email Geeks

What the documentation says

The foundational DMARC specification (RFC 7489) and subsequent guidance clearly define the hierarchy and inheritance rules for DMARC policies and reporting. Documentation typically highlights the default behavior where subdomains inherit the parent domain's policy and reporting destinations. However, it also emphasizes the overriding power of an explicit DMARC record published at the subdomain level, which allows for precise, independent control over that subdomain's email authentication posture and where its aggregate (RUA) and forensic (RUF) reports are sent.

Technical article

Documentation from DuoCircle states that the 'sp' tag allows domain owners to specify how DMARC should manage illegitimate emails sent from their subdomains. This tag provides a centralized mechanism for applying a DMARC policy to all subdomains that do not have their own, explicit DMARC record, enhancing control and simplifying management.

24 Apr 2024 - DuoCircle

Technical article

IETF Datatracker documentation indicates that DMARC policies are published by the Domain Owner or Policy Signer Organization (PSO) and retrieved by the Mail Receiver during the SMTP session, via the DNS. This highlights the fundamental role of DNS in DMARC's operation, serving as the lookup mechanism for policy and reporting instructions.

18 Jan 2024 - IETF Datatracker

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