Why are some emails failing DMARC checks even with correct SPF and DKIM alignment, and how can I troubleshoot it?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 May 2025
Updated 15 Aug 2025
11 min read
It can be perplexing when your emails consistently pass SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) authentication checks, yet still fail DMARC (Domain-based Message Authentication, Reporting, and Conformance). This scenario often leads to deliverability issues, with legitimate emails potentially ending up in spam folders or being rejected outright. Understanding why this happens requires a deeper dive into how DMARC works, particularly its reliance on identifier alignment, a concept distinct from basic SPF or DKIM pass/fail results.
DMARC leverages SPF and DKIM to verify the authenticity of an email, but it adds an extra layer of security: alignment. For an email to pass DMARC, at least one of these protocols (SPF or DKIM) must not only authenticate successfully but also have its domain align with the From header domain, which is the address visible to the recipient. Without this alignment, even a technically valid SPF record or DKIM signature can result in a DMARC failure.
This guide will walk you through the nuances of DMARC alignment, identify common causes for failures despite SPF and DKIM passing, and provide actionable troubleshooting steps to help ensure your emails reach their intended inboxes. We'll explore various scenarios, from third-party sending services to transient DNS issues, and equip you with the knowledge to diagnose and resolve these challenging deliverability problems.
The core reason emails fail DMARC despite passing SPF and DKIM is often due to a concept called identifier alignment. DMARC requires that the domain used in the SPF check (specifically the Return-Path or MailFrom domain) or the domain in the DKIM signature (d= tag) matches the domain in the From header of the email, which is what the recipient sees. If these domains do not match, even if SPF or DKIM technically pass, the email will fail DMARC alignment.
There are two modes of alignment: relaxed and strict. In relaxed mode, the organizational domains must match. For example, if your From header is sales@yourdomain.com, an SPF-authenticated domain of sub.yourdomain.com would achieve alignment. In strict mode, the domains must be an exact match. Many organizations start with relaxed alignment and move to strict alignment as their DMARC implementation matures.
This alignment requirement is why a DMARC failure can happen even when SPF and DKIM checks individually pass. It’s a crucial mechanism designed to prevent email spoofing, where an attacker might send emails appearing to be from your domain, even if they have SPF or DKIM set up for their own sending infrastructure. The alignment check ensures that the authenticated domain is indeed the one the recipient believes the email is coming from. If you're experiencing email deliverability issues, understanding this distinction is key to successful troubleshooting.
Common scenarios for misalignment
One of the most frequent reasons for DMARC alignment failures, even with proper SPF and DKIM setup, involves third-party sending services (ESPs). When you use a service like Kinsta or Postmark to send emails, they often handle the technical aspects of email sending, including the Return-Path address for SPF and the d= domain in the DKIM signature. These might default to the ESP's domain rather than your own, which will cause SPF or DKIM alignment to fail. Even if your SPF record is correctly configured to include the ESP's sending IPs, the Return-Path domain often points to their infrastructure (e.g., bounces.example-esp.com), breaking alignment with your From header domain.
Email forwarding is another common culprit. When an email is forwarded, it typically undergoes modifications that can break SPF alignment. The original SPF check validates the sender's IP against the Return-Path domain. However, when the email is forwarded, a new sending server (the forwarding server) is introduced. The forwarded email's Return-Path might then point to the forwarding server, which is usually not included in your domain's SPF record. This breaks SPF alignment, causing DMARC to fail based on SPF. DKIM, however, often remains intact during forwarding because the signature is tied to the message content, not the sending path, so it can still pass authentication and potentially DMARC if your DKIM is aligned.
Furthermore, some internal systems or specific transactional email flows might be configured in a way that inadvertently breaks alignment. This could include automated notifications, system alerts, or bounce messages that use a different MailFrom domain or don't properly sign with your domain's DKIM. For instance, systems like Google Workspace or Microsoft 365 might have specific configurations that need attention to ensure all mail flows align correctly. Recognizing these common scenarios is the first step in effective troubleshooting.
Beyond configuration: transient issues
Beyond configuration issues, transient network or DNS problems can sometimes cause seemingly random DMARC failures. Even if your SPF and DKIM records are perfectly set up, the receiving mail server needs to perform DNS lookups to validate them. If there are temporary connectivity issues, DNS resolution delays, or packet loss during these lookups, the authentication checks might fail, leading to a DMARC failure for that specific email, even if subsequent emails from the same source pass without issue. This is particularly relevant for DNS queries, which often rely on UDP and lack the error correction of TCP/IP.
Such sporadic failures are often difficult to pinpoint because they aren't tied to a persistent misconfiguration. They might manifest as a very small percentage of DMARC failures in your aggregate reports, coming from an IP address that otherwise sends DMARC-compliant emails. This suggests that the issue isn't with your setup, but rather with a momentary inability of the receiving server to complete the necessary DNS queries for SPF or DKIM validation. In some cases, the DNS provider itself might have rate limiting in place that could affect high-volume senders, though this is less common with enterprise-grade DNS services.
While these issues are often outside your direct control, understanding that they can occur is important for realistic expectations of DMARC compliance rates. It highlights why maintaining robust DNS infrastructure, ensuring all name servers are in sync, and selecting a reliable DNS provider can indirectly contribute to better DMARC pass rates. For more on DNS-related issues, you might find information on how DMARC authentication protocols work helpful, as many services operate in similar ways regarding DNS lookups.
Practical troubleshooting steps
To effectively troubleshoot DMARC failures, the most valuable resource is your DMARC reports. These XML-formatted reports provide aggregate data (RUA) and forensic data (RUF) on emails sent from your domain, indicating which messages passed or failed authentication and alignment, and why. Analyzing these reports helps you identify the source IPs sending on your behalf, the volume of emails, and the specific authentication results (SPF pass/fail, DKIM pass/fail, alignment pass/fail). For detailed guidance, exploring understanding and troubleshooting DMARC reports can provide deeper insights.
Beyond DMARC reports, direct email header analysis is critical for individual messages. When an email fails DMARC, retrieving the full email headers (e.g., from Gmail or Outlook) allows you to see the exact SPF and DKIM authentication results, including the domains used for alignment. Look for Authentication-Results headers which explicitly state spf=pass, dkim=pass, and then the dmarc=fail reason (e.g., header.from=example.com; domain.from=otherdomain.com). This information is invaluable for diagnosing alignment problems.
Header Field
Description
DMARC Relevance
From:
The visible sender address
This domain must align with the SPF or DKIM authenticated domain.
Return-Path:
The bounce address, checked by SPF.
The domain here must align with the From: header domain for SPF alignment.
DKIM-Signature:
Contains the d= (domain) tag.
The domain in the d= tag must align with the From: header domain for DKIM alignment.
Authentication-Results:
Summarizes all authentication checks.
Provides the overall DMARC verdict and reasons for failure.
Finally, ensure your DNS records for SPF and DKIM are correctly published and accessible. Common DNS issues include incorrect record syntax, exceeding the 10-lookup limit for SPF, or issues with DKIM selectors. Regularly checking your DNS health can prevent many intermittent DMARC failures. Tools can help you debug DMARC authentication issues, including SPF and DKIM problems.
Advanced considerations and solutions
When you encounter DMARC failures despite seemingly correct SPF and DKIM, it's easy to assume a misconfiguration on your end. However, as noted, a very small percentage of legitimate emails might fail due to factors beyond your direct control, such as transient DNS resolution issues or network glitches at the receiving end. DMARC is designed with these slight imperfections in mind; a few scattered failures, especially if SPF and DKIM are mostly passing, don't necessarily indicate a critical problem that requires immediate overhaul of your setup. The protocol inherently accepts that not every single email will pass 100% of the time.
For significant email volumes, such as millions of emails weekly, a few dozen DMARC failures might represent an extremely low percentage (e.g., 0.0005%). If these failures are sporadic and not concentrated from specific sending sources or to particular recipients, they might simply be noise. The critical aspect is to ensure the vast majority of your emails pass DMARC alignment. Continuous DMARC monitoring is key to differentiating between acceptable occasional failures and systemic issues.
Understanding DMARC policies
P=none: Emails that fail DMARC will still be delivered, but you receive reports. This is ideal for initial deployment and troubleshooting, allowing you to identify issues without impacting deliverability.
P=quarantine: Emails failing DMARC are sent to the recipient's spam folder. This is a step towards stronger protection, allowing you to test the impact before full rejection.
P=reject: Emails that fail DMARC are completely rejected at the SMTP layer and not delivered. This provides the highest level of protection against spoofing, but should only be used once you are confident in your DMARC compliance.
For ongoing vigilance, integrate DMARC reporting into your regular email deliverability checks. Tools that parse and visualize DMARC reports can provide clear insights, helping you spot trends or anomalies that indicate persistent issues requiring your attention. By understanding the nuances of DMARC and its inherent behaviors, you can better manage your email program and maintain high deliverability rates without overreacting to minor, expected failures. If you're encountering widespread issues, you may have more fundamental legitimate email failure problems.
Views from the trenches
Best practices
Always aim for both SPF and DKIM alignment to ensure redundancy in DMARC authentication.
Utilize DMARC aggregate reports (RUA) to monitor your email streams for authentication and alignment trends.
Configure a DMARC forensic report (RUF) address to receive samples of failed emails for deeper analysis.
When using third-party senders, configure custom return paths and DKIM keys to align with your domain.
Regularly check your DNS records for SPF and DKIM to prevent errors and ensure fast resolution times.
Common pitfalls
Assuming SPF and DKIM passing means DMARC will pass; alignment is a separate check.
Not accounting for email forwarding, which often breaks SPF alignment.
Ignoring DMARC reports, thus missing vital information on authentication failures.
Setting a DMARC policy to p=reject without thoroughly analyzing reports first.
Overlooking transient DNS issues or network problems as causes for sporadic failures.
Expert tips
Implement a DMARC policy gradually, starting with `p=none` to gather data before enforcing quarantine or reject.
Pay close attention to the `From` header domain; it is the central identifier for DMARC alignment.
For very low percentage failures, consider if they are acceptable anomalies due to the nature of email delivery.
Ensure your DNS resolvers are responsive and your name servers are synchronized for optimal performance.
If using services like Amazon SES, review their documentation for specific DMARC alignment best practices.
Marketer view
A marketer from Email Geeks says they found inconsistent reporting data, suggesting a system might be out of sync, leading to default settings being used for a small percentage of sends.
2021-02-02 - Email Geeks
Marketer view
A marketer from Email Geeks says they noticed a pattern where for every thousands of DMARC-compliant emails from the same IP, only one email failed DMARC checks, indicating a very low failure rate.
2021-02-02 - Email Geeks
Final thoughts on DMARC troubleshooting
Navigating DMARC failures, even when SPF and DKIM appear to be correctly configured, often boils down to understanding identifier alignment. This critical concept ensures that the visible From header domain matches the domain authenticated by SPF or DKIM. Common culprits include third-party sending services and email forwarding, which can alter the domains used for authentication. Additionally, transient network or DNS issues can lead to sporadic, unexplainable failures.
Effective troubleshooting involves diligently analyzing DMARC aggregate and forensic reports, examining email headers for granular authentication results, and regularly verifying your DNS records. While a small percentage of failures might be inherent to the email ecosystem, a proactive approach to monitoring and resolving identified issues will significantly improve your email deliverability and strengthen your domain's reputation.
