Summary
The optimal placement of DMARC records for subdomains is a common concern for domain owners aiming to secure their email infrastructure. While a DMARC record at the organizational (root) domain level with an sp tag can apply policies to all subdomains, there are specific scenarios where publishing individual DMARC records for subdomains is more beneficial. The choice depends heavily on administrative control, the diversity of email sending practices across subdomains, and the desired granularity of policy enforcement.
Key findings
- Inheritance: A subdomain without its own DMARC policy will automatically inherit the policy set on the parent domain, including the p and ruf or rua tags, unless an sp tag is present for subdomains. This is highlighted by eSecurity Planet.
- Granular control: Placing a DMARC record directly on a subdomain allows for a policy that is independent of the organizational domain's policy, providing more precise control over email authentication for specific sending purposes, such as marketing or transactional emails.
- Simplification: For simpler configurations, especially when administrative ownership is centralized, a single DMARC record at the organizational domain with an sp tag can be sufficient for managing all subdomains.
- Complexity management: Managing numerous individual DMARC records for many subdomains can become complex. A centralized record (with sp) can simplify this for certain setups.
Key considerations
- Administrative control: Consider who manages the domain and subdomain DNS records. Centralized control often favors a single organizational DMARC record, while distributed management might lean towards individual subdomain records.
- Policy differentiation: If different subdomains require distinct DMARC policies (e.g., p=none for some, p=reject for others), individual subdomain records are necessary. This aligns with overall DMARC, DKIM, and SPF setup best practices.
- Ease of management: Weigh the convenience of a single overarching policy against the flexibility of subdomain-specific policies. A simple guide to DMARC, SPF, and DKIM often recommends starting simple and expanding as needed.
- Future scalability: Anticipate future changes in your email sending infrastructure. If you plan to introduce many new subdomains with varying sending requirements, a flexible DMARC strategy that accommodates both root and subdomain level policies might be best.
What email marketers say
Email marketers often weigh the ease of managing DMARC for subdomains against the need for specific policy enforcement. The general consensus points towards a pragmatic approach, considering factors like organizational structure and the specific purpose of each subdomain's email traffic. Simplicity and clarity in configuration are highly valued, particularly when multiple subdomains are involved.
Key opinions
- Centralized preference: Many marketers prefer placing the DMARC record at the organizational domain with an sp= tag, as it feels more organized and simpler to understand quickly.
- Situational flexibility: There is no one-size-fits-all answer, and the best approach depends on specific organizational needs and administrative ownership of the domain. This aligns with Mailgun's approach to DMARC implementation.
- Policy variety: DMARC offers many options beyond just p=none, p=quarantine, or p=reject, allowing for nuanced control over subdomain policies.
Key considerations
- Organizational domain ownership: The decision often hinges on whether the team or individual has administrative ownership of the root domain. This dictates the level of control and ease of implementing a centralized DMARC record.
- Avoiding confusion: Having separate records for numerous different subdomains can lead to confusion and management overhead. A single record with the sp= tag for subdomains is often preferred for maintaining order.
- Policy rollout strategy: Marketers should consider how to safely transition DMARC policy to quarantine or reject across subdomains, whether through inheritance or specific subdomain records. This is critical for avoiding deliverability issues when moving beyond p=none.
- Understanding options: It's important to be aware of the full range of DMARC policy options available beyond just the basic policy directives, as these can offer additional flexibility for subdomain management. Marketers should know when to use p=none, p=quarantine, or p=reject.
Marketer view
Email marketer from Email Geeks notes that there isn't a universally correct answer for DMARC subdomain placement, as the ideal choice highly depends on an organization's specific needs and administrative control over the domain. This highlights the importance of evaluating individual circumstances.
Marketer view
Email marketer from Email Geeks expresses a preference for DMARC records to reside in the organizational domain. This approach is perceived as more organized and easier to grasp quickly, especially when utilizing the sp= tag for subdomains.
What the experts say
Experts in email deliverability emphasize that while a root domain DMARC record (with or without an sp tag) provides a baseline, specific scenarios necessitate dedicated DMARC records for subdomains. The key lies in understanding when and why to deviate from the inherited policy, particularly when dealing with diverse email sending profiles or delegated control.
Key opinions
- Organizational domain preference: Experts often recommend that the organizational domain should have a DMARC record, even if it's just p=none, to establish a baseline policy. This is a common starting point for understanding DMARC tags and their meanings.
- Independent policies: Publishing DMARC records for specific subdomains allows them to act independently of the organizational domain's policy, particularly if their policies differ. This is crucial for managing the distinct email streams that may originate from various subdomains.
- Subdomain policy inheritance: The sp (subdomain policy) tag within the organizational DMARC record allows a single policy to be applied to all subdomains that do not have their own explicit DMARC record. DuoCircle highlights how DMARC manages domains and subdomains through this mechanism.
Key considerations
- Policy differentiation: Consider whether different policies are required for different subdomains. For instance, a marketing subdomain might need a p=none policy for monitoring, while an internal communication subdomain could safely use p=reject.
- Alignment issues: Pay close attention to how SPF and DKIM alignment works with subdomains. Sometimes, DMARC authentication can fail even when SPF and DKIM pass due to domain alignment issues, and understanding why DMARC fails is crucial for subdomains.
- Delegated sending: If subdomains are used by third-party senders or different departments, allowing them to manage their own DMARC records (or inheriting a carefully chosen sp policy) can be more practical.
Expert view
Email expert from Email Geeks suggests that an organizational domain should ideally have a DMARC record, starting at least with p=none. This establishes a foundational policy for the entire domain hierarchy.
Expert view
Email expert from Email Geeks points out that publishing subdomain-specific policies is entirely possible and allows those policies to operate independently if they differ from the organizational domain's policy. This flexibility is key for complex email setups.
What the documentation says
Official DMARC documentation and industry guides provide clear instructions on how DMARC policies interact with subdomains. The core principle is inheritance, where a subdomain without its own DMARC record will follow the policy of its organizational parent. However, the documentation also outlines the explicit override capability, allowing for tailored policies when needed.
Key findings
- Default inheritance: If a subdomain does not have its own DMARC TXT record, it automatically inherits the DMARC policy from its parent (organizational) domain. This is a fundamental aspect of DMARC's design.
- Subdomain policy tag (sp): The sp tag in the organizational domain's DMARC record specifies the policy to be applied to all its subdomains. This policy takes precedence over the inherited p tag for subdomains.
- Explicit subdomain records: Publishing a DMARC record directly on a subdomain overrides any inherited or sp-defined policy from the organizational domain. This provides ultimate control at the subdomain level.
Key considerations
- DNS zone management: DMARC records are TXT records published in your domain's DNS zone. Understanding your DNS provider's interface (e.g., DNS Zone Editor) is essential for proper placement, as detailed by SiteGround.
- Policy choice: The policy chosen (none, quarantine, reject) for the organizational domain and any sp tag, or for individual subdomains, should align with the organization's risk tolerance and email sending maturity. Refer to DMARC record and policy examples.
- Comprehensive authentication: DMARC relies on SPF and DKIM for authentication. Ensuring these protocols are correctly configured for all sending sources, including those on subdomains, is paramount for DMARC to function effectively. Consult resources on where SPF, DKIM, and DMARC records should be placed.
Technical article
Documentation from Kickbox Blog clarifies that a DMARC DNS record applied to a domain (organizational) also affects any subdomains, unless a subdomain has its own DMARC DNS record. This confirms the inheritance behavior of DMARC policies.
Technical article
Documentation from VerifyDMARC.com emphasizes that a DMARC DNS record applied to a domain will affect any subdomains unless that specific subdomain has its own DMARC record. This provides clear guidance on how to establish unique policies.
Related resources
10 resources
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