How does relaxed domain alignment work in DMARC and SPF?

Key findings

• Organizational domain match: In relaxed alignment, two hostnames are considered aligned if they share the same organizational (parent) domain. For example, subdomain1.domain.com and subdomain2.domain.com would be aligned.
• DMARC specific concept: SPF itself does not have a concept of 'alignment' or 'inheritance'. Alignment is a DMARC feature that evaluates the relationship between SPF's authenticated domain and the Header From domain.
• Flexibility for subdomains: Relaxed alignment is particularly useful for organizations that send emails from various subdomains, as it prevents DMARC failures for legitimate mail. This is detailed in guides like DMARC Relaxed Vs Strict Alignment.
• No impact on SPF authentication: Relaxed alignment doesn't change how SPF itself authenticates. SPF still checks if the sending IP is authorized for the Return-Path domain. If that domain doesn't have an SPF record, it won't check parent domains.
• DMARC pass criteria: For an email to pass DMARC with relaxed alignment, either SPF or DKIM must pass authentication, and their respective domains (Return-Path for SPF, d= for DKIM) must align with the Header From domain at the organizational level.

Key considerations

• Default setting: Many DMARC implementations default to relaxed alignment because it offers greater compatibility with diverse sending infrastructures, including third-party email service providers (ESPs).
• Security vs. flexibility: While relaxed alignment provides flexibility, strict alignment offers a higher level of security by requiring an exact domain match. The choice depends on your sending ecosystem and security posture. Read more about this choice in DMARC alignment strict vs relaxed.
• Google Postmaster Tools (GPT) reporting: GPT reports SPF passing based on SPF authentication itself, but for DMARC SPF alignment, it considers if the SPF domain is aligned with the From address domain. This can sometimes lead to confusion. Learn more about understanding Google Postmaster Tools.
• Subdomain management: Even with relaxed alignment, ensure that subdomains used in the Return-Path or DKIM d= tag are properly configured with their own SPF and DKIM records if needed, to avoid authentication issues.

Key opinions

• Subdomain flexibility: Many marketers confirm that relaxed alignment allows subdomains (e.g., subdomain1.domain.com and subdomain3.domain.com) to be aligned as long as they share the same parent organizational domain.
• DMARC's alignment role: Marketers frequently emphasize that alignment is a DMARC-specific concept, not a native feature of SPF itself. SPF simply authenticates the Return-Path domain. This is essential for understanding how SPF, DKIM, and DMARC interact.
• Practicality for senders: Relaxed alignment is generally seen as the more practical choice for many email marketers, particularly those using various sending platforms that might use subdomains for the MailFrom (Return-Path) or DKIM signature. This is discussed in DMARC relaxed alignment for SPF/DKIM.
• Google Postmaster Tools perception: There is an observation that Google Postmaster Tools reports SPF as passing only if the SPF domain aligns with the From address domain, which aligns with DMARC's interpretation of SPF.

Key considerations

• Configuration accuracy: Even with relaxed alignment, ensure that your SPF and DKIM records are correctly published for all sending domains and subdomains to prevent authentication failures. Incorrect configuration can lead to DMARC authentication issues.
• DMARC policy rollout: When implementing DMARC, starting with a relaxed policy (p=none or p=quarantine with relaxed alignment) allows for monitoring and adjustments before moving to a stricter enforcement like p=reject.
• Deliverability impact: While relaxed alignment aids in passing DMARC, consistently ensuring both SPF and DKIM pass and align is key for optimal inbox placement. Consider how bad SPF alignment affects deliverability overall.
• Third-party senders: Many ESPs or transactional email services use their own domains or subdomains for the Return-Path. Relaxed alignment is crucial in these scenarios to ensure your emails pass DMARC and aren't blocked, even if the subdomains don't exactly match your Header From domain.

Key opinions

• DMARC-specific requirement: Experts universally agree that SPF alignment is a DMARC feature, not an inherent part of SPF's authentication process. SPF determines if the MailFrom domain is authorized to send, while DMARC checks if that authenticated domain aligns with the Header From domain.
• Organizational domain focus: For relaxed alignment, the key is that the organizational domain (e.g., example.com for sub.example.com) must match. This allows for flexibility across subdomains without failing DMARC.
• Common industry practice: Relaxed alignment is a widely adopted standard, especially for large organizations or those relying on third-party senders, as it simplifies compliance without sacrificing significant security. This is often preferred, as highlighted in SPF and DKIM Identifiers Aligned.
• Balancing security and deliverability: While strict alignment offers maximum protection against spoofing, relaxed alignment provides a pragmatic balance, ensuring deliverability for legitimate mail flows that might otherwise fail DMARC.

Key considerations

• Potential for broader spoofing: While relaxed alignment aids legitimate senders, it theoretically allows a slightly broader range of spoofing if only SPF or DKIM is aligned and the organizational domain is consistent. However, DMARC's policy (quarantine or reject) mitigates this risk.
• Subdomain SPF records: Even with relaxed DMARC alignment, SPF records must exist for the specific subdomain used as the Return-Path. If a subdomain lacks an SPF record, SPF authentication for that particular subdomain will fail.
• DMARC record configuration: To enable relaxed SPF alignment, the DMARC record should specify aspf=r; (or be omitted, as 'r' is often the default). Similarly, for DKIM, adkim=r; is used.
• Monitoring reports: Regardless of the alignment mode chosen, regularly reviewing DMARC aggregate and forensic reports is essential to identify any alignment failures and debug issues. This helps ensure your emails are not blocklisted unnecessarily.

Key findings

• Definition of relaxed alignment: Documentation specifies that relaxed alignment permits a match between the organizational domain of the Header From address and the SPF or DKIM authenticated domain. This is often the default or preferred mode for flexibility.
• Configuration in DMARC record: Documentation outlines how to configure relaxed alignment using the DMARC tags aspf=r; for SPF and adkim=r; for DKIM within the DMARC record. For SPF, omitting the tag usually implies relaxed alignment as the default. More on DMARC tags.
• Impact on DMARC pass: Documentation clarifies that if either SPF or DKIM passes authentication and achieves relaxed alignment, the email will pass the DMARC check. This means one passing method is sufficient.
• Subdomain handling: A key finding is that relaxed mode specifically accommodates subdomains, allowing them to pass DMARC as long as they fall under the same organizational domain as the Header From address.

Key considerations

• Understanding organizational domain: Technical documentation is essential for correctly identifying the 'organizational domain' (or effective second-level domain) which is the basis for relaxed alignment matching. This often involves looking at public suffix lists.
• Coexistence with strict alignment: Documentation explains that DMARC can be set to either strict or relaxed alignment, and the choice impacts how tightly the domains must match. Strict (aspf=s;) requires an exact match for SPF, including subdomains.
• Best practices for deployment: Documentation often recommends starting with relaxed alignment, especially when first deploying DMARC, to minimize impact on legitimate mail flows while gaining visibility into sending patterns. For further reading, check safely transition DMARC policy.
• DMARC report interpretation: Documentation is vital for interpreting DMARC reports, which indicate whether SPF and DKIM passed authentication and, crucially, whether they achieved alignment (relaxed or strict) with the Header From domain. This helps in troubleshooting DMARC reports.