How to concisely explain DMARC passing and identifier alignment?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 Jun 2025
Updated 13 Oct 2025
8 min read
Explaining DMARC, especially the concept of identifier alignment, can often feel like a deep dive into technical jargon. It's easy to get lost in the nuances of various "From" addresses and authentication protocols. My goal here is to distill this complex topic into a clear, understandable explanation, focusing on what truly matters for DMARC to pass and for your emails to reach their intended inboxes securely.
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, is a vital email security protocol. It builds upon two older standards, SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), to help protect your domain from impersonation and phishing. Essentially, SPF and DKIM provide methods for a sender to declare responsibility for an email, while DMARC allows a domain owner to specify how email receivers should handle messages that claim to be from their domain.
For DMARC to authenticate an email successfully, at least one of these underlying mechanisms (SPF or DKIM) must "pass" its respective check. This means the email must either come from an IP address authorized in the domain's SPF record, or it must carry a valid cryptographic signature that matches the domain in its DKIM record. However, merely passing SPF or DKIM is only half the story.
The real magic of DMARC, and where many find the explanation challenging, lies in its requirement for "identifier alignment." Without proper alignment, an email might pass SPF or DKIM, but still fail DMARC, which can lead to deliverability issues and confusion. Understanding this alignment is crucial for ensuring your emails are not only authenticated but also treated as legitimate by recipient mail servers.
Decoding identifier alignment
Identifier alignment, in simple terms, means that the domain verified by SPF or DKIM must "align" with the domain that the recipient sees in the "From" header of the email. It's about ensuring that the domain taking responsibility for the email (via SPF or DKIM) is indeed the same one the user believes the email is from. This prevents scenarios where a legitimate sender's infrastructure is used to send spoofed emails. You can find a comprehensive explanation of DMARC identifier alignment from DMARCLY.
There are two types of alignment: SPF alignment and DKIM alignment. For SPF alignment, the domain in the "Return-Path" (also known as the "envelope from" or "MailFrom") must match the domain in the "From" header. For DKIM alignment, the d= tag in the DKIM signature must match the domain in the "From" header. This concept is further refined by "strict" and "relaxed" alignment modes.
Relaxed alignment allows a subdomain of the organizational domain to align, for example, mail.example.com aligning with example.com. Strict alignment, on the other hand, requires an exact match between the domains. You can learn more about how relaxed domain alignment works by checking our guide. Most DMARC implementations use relaxed alignment by default, offering more flexibility, but strict alignment provides stronger protection against subtle spoofing attempts.
Strict alignment
Requirements: Exact domain match required for both SPF and DKIM. No subdomains are allowed to align with the organizational domain.
Security: Offers the highest level of security, making it harder for attackers to spoof emails using subdomains.
Relaxed alignment
Requirements: Allows subdomains to align with the organizational domain, e.g., mail.example.com aligning with example.com.
Flexibility: Provides greater flexibility for organizations that use various subdomains for different sending purposes.
How an email passes DMARC, step-by-step
An email passes DMARC if it satisfies a specific set of conditions. First, either SPF or DKIM must pass its individual authentication check. Second, for the mechanism that passed, its authenticated domain must align with the "From" header domain. If both SPF and DKIM pass and align, that's even better, but DMARC only requires one of them to meet both criteria.
This "OR logic with AND alignment" is critical. For instance, an email might pass SPF because the sending IP is authorized, but if the Return-Path domain doesn't align with the From header domain, DMARC will fail for SPF. The same applies to DKIM; a valid DKIM signature isn't enough if its d= domain doesn't align with the From header domain. This interaction is key to DMARC's effectiveness in preventing domain abuse. You can find more detailed information on DMARC architecture and identifier alignment in Cisco's documentation.
When DMARC passes, the receiving email server knows that the email is legitimate and originated from an authorized source that aligns with the visible sender. If DMARC fails, the receiver will apply the policy specified in the sender's DMARC record, which can be p=none (monitor), p=quarantine (move to spam/junk), or p=reject (block delivery entirely). This means a DMARC failure can significantly impact your email deliverability, highlighting why understanding and achieving how to debug DMARC authentication failure is crucial. It’s also why DMARC is so important to protect your domain reputation.
Simplified DMARC checkPseudocode
IF ( (SPF_PASS AND SPF_ALIGN) OR (DKIM_PASS AND DKIM_ALIGN) )
THEN DMARC_PASS
ELSE
DMARC_FAIL
END IF
The visible "From" header: what the user sees
At the heart of identifier alignment is the "From" header, or Header From. This is the domain that email recipients actually see in their inbox. When you receive an email from marketing@example.com, example.com is the Header From domain. DMARC's primary purpose is to ensure that this visible From domain is genuinely authorized to send mail.
This distinction is crucial because other domains might be involved in an email's journey. For instance, the Return-Path domain (used for SPF checks) might be a sending service's domain, like bounce.somesender.net, while your visible From domain is yourdomain.com. For DMARC to pass via SPF, somesender.net (or a subdomain) would need to align with yourdomain.com under a relaxed policy, or yourdomain.com itself would need to be the Return-Path domain under a strict policy. If you have SPF not aligned in a DMARC report, it can severely impact deliverability.
Similarly, with DKIM, the domain specified in the d= tag of the DKIM signature could be somesender.net if you're using a third-party email service provider. For DKIM alignment to pass, somesender.net (or a subdomain) would need to align with your Header From domain (yourdomain.com). This is where careful configuration of your email service providers and DMARC settings becomes essential.
The primary impact of alignment
The Header From domain is what your recipients see and trust. DMARC ensures that this visible sender identity is authenticated, preventing malicious actors from using your brand to send phishing or spam emails.
Trust: Ensures that the sender domain users see is legitimately associated with the email.
Brand Protection: Protects your brand's reputation by preventing unauthorized use of your domain in the From field.
User Experience: Reduces the likelihood of your legitimate emails being flagged as spam or rejected by recipient servers.
Monitoring and refining your DMARC setup
Effectively managing DMARC means regularly monitoring your email traffic to identify any authentication or alignment failures. DMARC reports, specifically aggregate (RUA) reports, provide invaluable insights into who is sending email purporting to be from your domain, whether SPF and DKIM are passing, and crucially, whether they are aligning correctly. Without these reports, it's virtually impossible to know if your DMARC policy is working as intended or if legitimate emails are failing.
Suped offers comprehensive DMARC monitoring and reporting capabilities, making it easy to visualize your DMARC compliance. By analyzing detailed reports, you can quickly identify sources of non-compliance, troubleshoot alignment issues, and safely transition your DMARC policy to quarantine or reject. This proactive approach is key to bolstering your email security and ensuring optimal deliverability.
Views from the trenches
Best practices
Always start with a DMARC policy of p=none to gather reports and understand your email ecosystem.
Regularly review DMARC aggregate reports to identify legitimate sending sources and correct alignment issues.
Ensure all third-party email senders are properly configured with SPF and DKIM for alignment.
Educate your team on DMARC's importance and the potential impact of misconfigurations.
Common pitfalls
Implementing a p=quarantine or p=reject policy without first analyzing DMARC reports.
Overlooking legitimate sending services not yet DMARC compliant, leading to deliverability failures.
Not understanding the difference between SPF Return-Path and DKIM d= domains for alignment.
Ignoring DMARC reports, thus missing critical insights into authentication and spoofing attempts.
Expert tips
Tailor the depth of technical detail to your audience's understanding level to avoid unnecessary jargon.
Utilize visual aids, such as DMARC reporting dashboards, to demonstrate alignment and authentication status.
Focus the explanation on the "From" header domain, as it is what recipients see and is central to DMARC's function.
Start with the core concept: either SPF or DKIM must pass and align with the visible "From" domain.
Expert view
Expert from Email Geeks says: DKIM and SPF allow a sender to claim responsibility for an email, while DMARC empowers a domain owner to assert responsibility for all emails sent from their domain via DKIM or SPF.
2019-07-30 - Email Geeks
Expert view
Expert from Email Geeks says: Identifier alignment is essentially a technical way of saying the domain is obviously the same.
2019-07-30 - Email Geeks
Simplifying DMARC for better email security
Explaining DMARC passing and identifier alignment doesn't have to be a daunting task. By focusing on the core principle that either SPF or DKIM must pass and their respective domains must align with the visible "From" header, you can communicate its essence effectively. This dual requirement ensures that only authorized senders can use your domain, significantly enhancing your email security posture and deliverability.
