How to concisely explain DMARC passing and identifier alignment?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 Jun 2025
Updated 19 Aug 2025
6 min read
Explaining DMARC, particularly the concept of identifier alignment, can often feel like navigating a dense jungle. We want to be thorough, but it's easy to get bogged down in technical details like SPF and DKIM domains versus the header From address. However, a clear and concise explanation is essential for anyone dealing with email deliverability, from marketers to system administrators.
The goal is to provide enough information for a solid understanding without overwhelming the audience with unnecessary technical minutiae. This guide focuses on breaking down DMARC passing and identifier alignment into easily digestible concepts.
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, is an email authentication protocol that helps protect against email spoofing, phishing, and other cyber threats. It builds upon two existing standards, SPF and DKIM, providing a framework for domain owners to specify how receiving mail servers should handle emails that fail authentication checks. Essentially, DMARC tells recipients whether an email from your domain is legitimate or not.
For an email to pass DMARC, at least one of these underlying authentication mechanisms (SPF or DKIM) must not only pass its own check but also demonstrate identifier alignment. This means the domain used for SPF or DKIM authentication must match the domain in the email's From header, which is the address visible to the recipient. Without this alignment, even if SPF or DKIM technically passes, DMARC will fail.
Think of it as a bouncer at a club. SPF and DKIM are like showing an ID and a ticket. DMARC is the bouncer who says, "Great, but do the name on the ID or the name on the ticket match the name you used to book the VIP table?" If they don't, you're not getting in, even if your ID and ticket are otherwise valid. This analogy helps simplify the intricate interplay between the different authentication layers.
The core of identifier alignment
Identifier alignment is the crucial link that connects SPF and DKIM authentication results to the email's visible From header domain. This ensures that the domain claiming responsibility for sending the email is indeed the one the recipient sees. There are two types of alignment: strict and relaxed.
In strict alignment, the domains must be an exact match. For example, if your From header is example.com, the SPF authenticated domain (envelope from) must also be example.com, and the DKIM signing domain must also be example.com. This provides the highest level of security. Conversely, relaxed alignment allows for subdomain matches. For instance, if your From header is example.com, an SPF or DKIM domain of mail.example.com would still pass alignment. You can learn more about how DMARC architecture and identifier alignment works directly from authoritative sources like Cisco.
The choice between strict and relaxed alignment depends on your email sending infrastructure and security needs. While strict alignment offers stronger protection, relaxed alignment can be more forgiving for complex sending setups involving third-party senders. It's a key factor in ensuring your emails consistently pass DMARC checks, preventing them from being blocked or sent to spam.
SPF alignment
Domain check: The domain in the Return-Path (or envelope from) header must align with the From header domain.
Alignment type: Can be strict (exact match) or relaxed (subdomain allowed).
DKIM alignment
Domain check: The domain in the DKIM signature (d=tag) must align with the From header domain.
Alignment type: Can be strict (exact match) or relaxed (subdomain allowed).
How DMARC passes: the 'or' logic
A crucial point about DMARC passing is its OR logic. For DMARC to pass, an email only needs to satisfy either SPF authentication with alignment or DKIM authentication with alignment. It doesn't require both to pass and align, which is a common misconception.
This flexibility is vital for various sending scenarios. For example, if you send marketing emails through a third-party provider, they might handle the DKIM signing, while your transactional emails use your own SPF records. As long as one of these authentications passes and aligns with your visible From domain, the email will satisfy DMARC's requirements. This is why understanding the interplay of DMARC, SPF, and DKIM is so important for robust email security.
The choice of which mechanism to rely on depends heavily on your specific email setup and the capabilities of your email service provider. Many organizations aim for both to pass and align to provide maximum coverage and resilience, but it's not a strict DMARC requirement for a pass.
Common pitfalls and troubleshooting tips
Despite a correct SPF or DKIM setup, emails can still fail DMARC if identifier alignment is overlooked. This is a common pitfall that often leads to DMARC authentication failures. One of the best ways to diagnose these issues is through DMARC reports.
These reports provide valuable insights into your email traffic, showing which emails passed or failed DMARC, why they failed (e.g., SPF alignment failure, DKIM failure), and from which source IPs. Monitoring these reports is critical for identifying misconfigurations and ensuring your legitimate emails reach their intended recipients without being caught in spam filters or being blocklisted (or blacklisted). If you're encountering failures, consult your DMARC debugging guide for detailed troubleshooting steps.
For instances where SPF alignment specifically causes issues, understand what an unaligned SPF record means for your deliverability. Regularly reviewing your DMARC record settings and policies is an ongoing process to maintain strong email authentication.
Views from the trenches
Best practices
Ensure SPF and DKIM are correctly configured on your sending domains before implementing DMARC policies.
Start with a DMARC policy of p=none to monitor reports and identify legitimate sending sources.
Gradually move to p=quarantine, then p=reject, as you gain confidence in your DMARC compliance.
Regularly review your DMARC aggregate and forensic reports to detect authentication failures.
Aim for both SPF and DKIM to pass alignment for maximum redundancy and improved deliverability.
Educate your team on DMARC's importance and how it affects email deliverability and security.
Common pitfalls
Forgetting to update SPF records when adding new sending services, leading to SPF failures.
Using relaxed alignment (adspf=r or adkim=r) too broadly, which weakens protection against spoofing.
Moving to p=reject without thoroughly analyzing DMARC reports, causing legitimate emails to be blocked.
Ignoring DMARC reports, missing critical insights into email authentication issues.
Not aligning subdomains with the organizational domain, causing DMARC failures for legitimate emails.
Assuming DMARC passes if SPF or DKIM passes, overlooking the identifier alignment requirement.
Expert tips
When explaining DMARC, focus on the 'From' header and its need to align with either the SPF or DKIM authenticated domain, using clear analogies.
Emphasize that DMARC is not about *just* SPF or DKIM passing, but about the *identity* behind the email.
Show, don't just tell. Use real DMARC report data to illustrate alignment or misalignment issues.
Consider relaxed alignment for third-party senders where strict alignment is difficult to achieve.
DMARC requires either SPF or DKIM to pass *and* align with the visible From domain, it's an 'OR' logic for authentication but an 'AND' for alignment check.
Remember that DMARC's primary goal is to prevent unauthorized use of your domain in the 'From' address.
Expert view
Expert from Email Geeks says: DKIM and SPF are ways for a sender to assert responsibility for an email, while DMARC allows a domain owner to specify responsibility for all mail sent from their domain via these mechanisms.
2023-01-20 - Email Geeks
Expert view
Expert from Email Geeks says: Identifier alignment is fundamentally a technical definition that ensures the domain used for authentication is clearly the same as the domain shown in the email's From header.
2023-02-15 - Email Geeks
Simplifying DMARC for better email security
Effectively explaining DMARC passing and identifier alignment boils down to simplifying complex concepts without losing their core meaning. Remember, DMARC's purpose is to verify the legitimacy of the From domain by checking if either SPF or DKIM successfully authenticates and aligns with it.
By focusing on the 'OR' logic for authentication and the critical role of alignment with the visible From header, you can demystify DMARC for anyone, ensuring better understanding and, ultimately, improved email security and deliverability for your organization. Continued monitoring of your DMARC policies is key to maintaining a strong email sender reputation.
