How to debug DMARC authentication failure and alignment issues?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 16 Aug 2025
9 min read
Email deliverability relies heavily on proper authentication, and DMARC (Domain-based Message Authentication, Reporting & Conformance) is a critical standard. When DMARC authentication fails or alignment issues arise, it can severely impact whether your emails land in the inbox or are redirected to spam, or even rejected entirely. Debugging these issues requires a systematic approach, often starting with understanding the reports generated by receiving mail servers. This guide will walk you through the process of diagnosing and resolving DMARC authentication and alignment problems.
When an email “fails” DMARC, it means it did not pass the checks set by your DMARC policy. This typically happens if the email’s SPF (Sender Policy Framework) or DKIM (DomainKeys Identified Mail) authentication does not pass, or if it passes authentication but fails DMARC’s alignment requirements. DMARC requires that the domain used in the “From” header of the email, which is what recipients see, matches (aligns) with the domain authenticated by SPF or DKIM.
SPF alignment occurs when the domain in the “Return-Path” (also known as the “MAIL FROM” or “envelope From”) matches the “From” header domain. DKIM alignment occurs when the domain that cryptographically signed the email matches the “From” header domain. These matches can be “strict” (exact match) or “relaxed” (subdomain match), as defined in your DMARC record. A common pitfall (or cause of a DMARC failure) is when emails are sent via third-party services whose domains do not align with your “From” header domain.
Even if SPF and DKIM records are correctly published and valid, DMARC can still fail due to these alignment issues. For example, if your SPF record authorizes a third-party sender, but that sender uses their own domain in the “Return-Path” instead of your domain or a subdomain, then SPF authentication might pass, but SPF alignment (and thus DMARC) will fail. It is crucial to understand these nuances to pinpoint exactly why emails are not passing DMARC. You can read more about why DMARC authentication fails in another resource.
Furthermore, a DMARC failure can send your emails directly to the spam folder, or cause them to be rejected outright. This affects your email deliverability rates and can damage your sender reputation over time. Understanding these underlying mechanisms is the first step towards effective troubleshooting.
Decoding DMARC reports
The most powerful tool for debugging DMARC issues is the DMARC report. These XML files are sent to the email address specified in the rua (aggregate reports) or ruf (forensic reports) tags of your DMARC record. Aggregate reports provide an overview of all mail sent using your domain, including how many messages passed or failed authentication and alignment, and from which IP addresses. Forensic reports, while less commonly used due to privacy concerns, offer more detailed information about individual failed messages.
Aggregate reports are invaluable for identifying the source of unauthenticated or misaligned emails. They break down sending sources by IP address, showing their SPF and DKIM authentication results and whether they achieved DMARC alignment. Regularly analyzing these reports helps you detect unauthorized use of your domain and identify legitimate sending services that are not properly aligning with your DMARC policy.
When reviewing these reports, pay close attention to the source_ip and disposition fields. A disposition of “none”, “quarantine”, or “reject” indicates the action taken by the receiving server based on your DMARC policy. If you see legitimate email streams with a high percentage of “fail” results for spf_pass or dkim_pass and alignment, it points directly to an authentication or alignment problem. Refer to RFC 7489 for the official DMARC specification.
To receive these reports, ensure your DMARC record includes the rua tag. This record instructs receiving servers to send aggregate reports to your specified email address and also specifies fo=1 to request forensic reports on all failures, regardless of policy. Understanding the different DMARC tags and their meanings is crucial for effective implementation.
Common causes and resolutions
DMARC authentication or alignment failures often stem from a few recurring issues. Identifying the root cause is the first step towards a solution.
Let us look at some common scenarios:
Causes
Solutions
Misconfigured SPF or DKIM records
Update your SPF record to include all legitimate sending IPs and correct any syntax errors. Ensure DKIM keys are correctly published and rotated. Check out a guide to how to fix common DMARC issues in Microsoft 365 and Google Workspace.
Third-party sending services
Many email service providers (ESPs) send emails on your behalf. If their setup does not align the “From” header with your domain, DMARC will fail.
Email forwarding
When an email is forwarded, the “Return-Path” often changes, breaking SPF alignment. This is a common reason why DMARC fails when SPF and DKIM appear correct.
Subdomain usage
If you send from a subdomain (e.g., marketing.example.com) but your SPF or DKIM alignment settings are strict (aspf=s or adkim=s), it can cause failures if the “From” header does not strictly match the authenticated domain.
Missing DMARC record
Without a DMARC record, receiving servers cannot check for DMARC compliance, leaving your domain vulnerable to spoofing.
Incorrect DMARC policy
A p=reject or p=quarantine policy enforced too early, before all legitimate sources are aligned, will cause deliverability issues.
When using third-party services, it is vital to ensure they are configured to send emails in a way that allows for DMARC alignment. This usually involves setting up a custom domain for sending or ensuring they use your domain in the 'envelope from' (for SPF) or sign with your domain (for DKIM). If you are seeing authentication failures from third-party senders, refer to their documentation or support to configure alignment correctly. For example, some platforms might offer options for custom “Return-Path” domains or allow you to use your own DKIM keys.
Email forwarding is a trickier issue, as it is often beyond your control. While DMARC is designed to handle this, it can still lead to legitimate emails failing. In such cases, the p=none policy on your DMARC record allows emails to be delivered while you gather reports. If your DMARC policy is set to p=reject, forwarded emails might not reach their destination. For more details on this, you can look up how Google troubleshoots DMARC issues.
For p=reject policies, a key step is to analyze your DMARC reports to identify all legitimate sending sources and ensure they pass both authentication and alignment before enforcing a strict policy. If you are encountering issues with a p=reject policy, understanding how to troubleshoot DMARC reject policies is essential.
Systematic debugging strategies
Debugging DMARC is a process of elimination and careful analysis. Once you understand the basics of reports, you can apply a systematic approach to identify and resolve issues.
Review DMARC reports thoroughly: Start by examining your aggregate DMARC reports. These reports are your primary source of truth, providing insights into which sources are sending on your behalf and whether those emails are passing or failing DMARC authentication and alignment. Pay attention to the volume of failed emails and the IP addresses associated with them. This helps you diagnose DMARC failures using DMARC reports effectively.
Check DNS records: Even if you believe your DNS records are stable, verify the SPF and DKIM records for the domains reported as failing. Ensure there are no syntax errors, that all legitimate sending IPs are included in your SPF record, and that your DKIM keys are valid and published correctly in DNS. Sometimes, a seemingly small misconfiguration can cause significant problems. You can learn how to set up and troubleshoot SPF, DKIM, and DMARC for your domain.
Analyze email headers: For individual emails that you suspect are failing, analyze their full headers. Look for the Authentication-Results header, which provides a detailed breakdown of SPF, DKIM, and DMARC checks performed by the receiving server. This header will explicitly state “pass” or “fail” for each authentication method and indicate alignment status.
Gradually enforce your DMARC policy: If you are just starting with DMARC or encountering persistent issues, begin with a p=none policy. This allows all emails to be delivered while you gather data and fix issues without impacting deliverability. Once you are confident that all legitimate traffic is aligning, you can gradually move to p=quarantine (deliver to spam/junk) and then p=reject (block delivery). This phased approach helps troubleshoot DMARC failures and their impact on email deliverability. More details on how to safely transition your DMARC policy can be found in our guides.
Views from the trenches
Best practices
Always start your DMARC implementation with a p=none policy to gather data and identify all legitimate sending sources without affecting email delivery.
Regularly audit your sending infrastructure and third-party services to ensure they adhere to DMARC alignment requirements, as configurations can change over time.
Common pitfalls
Ignoring rua reports or failing to process them, which leaves you blind to authentication and alignment issues.
Enforcing a p=reject policy too early, before all legitimate email streams are fully DMARC compliant, leading to deliverability problems.
Expert tips
Leverage DMARC aggregate reports to quickly identify unauthorized senders spoofing your domain and take action.
When troubleshooting, prioritize fixing alignment issues for high-volume legitimate senders first, as these have the biggest impact on your deliverability.
Marketer view
Marketer from Email Geeks says: DMARC aggregate reports are the most reliable tool for understanding why DMARC authentication might be failing for certain email streams.
February 16, 2022 - Email Geeks
Marketer view
Marketer from Email Geeks says: When diagnosing DMARC failures, focusing on the actual XML reports generated by Internet Service Providers helps verify SPF and DKIM alignment for specific IP addresses and sources.
February 16, 2022 - Email Geeks
Ensuring your emails are secure
Debugging DMARC authentication and alignment failures is a continuous process that requires attention to detail and ongoing monitoring. By leveraging DMARC reports, meticulously checking your DNS records for SPF and DKIM, and understanding the nuances of alignment, you can effectively resolve most issues. Maintaining a healthy email ecosystem safeguards your domain’s reputation, improves deliverability, and protects your brand from phishing and spoofing attacks. For an overview of DMARC authentication, you can check out the DMARC.org overview.
Microsoft 365 and Google Workspace.
