Why is DMARC failing for an alias domain despite expected DKIM alignment?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Nov 2025
Updated 15 Nov 2025
7 min read
Dealing with DMARC failures can be a frustrating experience, especially when you think you've done everything right. It's even more perplexing when you're sending from an alias domain in Google Workspace, and it seems like your DKIM is aligned. I recently encountered a scenario where the DMARC record was failing, despite SPF passing for the return-path domain and a DKIM signature existing for the header domain. This often comes down to a nuanced understanding of DMARC alignment.
The problem lies not in the mere presence of SPF or DKIM, but in how their domains align with the 'From' header domain. Alias domains in services like Google Workspace add a layer of complexity, often affecting how authentication protocols like SPF and DKIM are handled. This can lead to unexpected DMARC failures, even when individual checks appear to pass.
A common symptom is seeing an Authentication-Results header with spf=pass and dkim=fail (no key for signature), even when a DKIM record exists for the 'From' domain. This points to a deeper issue with how the receiving server interprets the various domains involved in email authentication.
Understanding DMARC alignment
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, builds upon SPF and DKIM by enforcing alignment. For DMARC to pass, at least one of these protocols must align with the 'From' header domain. This means the domain used in the SPF check (the smtp.mailfrom or envelope sender) or the domain in the DKIM signature's d= tag must match the From header domain.
When sending from an alias domain, the smtp.mailfrom (or return-path) often defaults to the primary domain of your email provider, like Google. This means that while SPF might pass for the return-path domain, it won't align with your alias domain in the From header. Consequently, SPF DMARC alignment fails. For DKIM alignment, the d= tag in the DKIM signature must match the From header domain for DMARC to pass.
The key takeaway here is that passing SPF or DKIM alone isn't enough, they must also align with the domain you're trying to protect with DMARC. This is a common pitfall for organizations using alias domains without proper configuration.
The puzzle of alias domains in Google Workspace
DMARC requires either SPF or DKIM to align with the From: header domain. If your alias setup causes the envelope sender (for SPF) or the DKIM signing domain to differ from your visible sending domain, DMARC will fail.
When you send an email from an alias domain in Google Workspace, the smtp.mailfrom address, which is checked by SPF, typically uses your primary Google Workspace domain, not the alias. This means that while SPF might pass for your primary domain, it inherently won't achieve alignment with the alias domain in the From header.
The situation becomes trickier with DKIM. Google Workspace will typically sign outgoing mail with a DKIM key belonging to the domain of the actual mailbox, not necessarily the alias. This means the d= tag in your DKIM signature might not match the alias domain in the From header. Even if a valid DKIM record exists for your alias domain, it won't be used for signing by Google, leading to a DKIM DMARC alignment failure. This is often the root cause of DMARC failing when SPF and DKIM pass.
SPF alignment challenges
Envelope sender mismatch: When sending from an alias, the smtp.mailfrom often uses the primary domain, not the alias.
Lack of direct control: Email providers typically manage the envelope sender, making direct SPF alignment for alias domains difficult.
DKIM alignment solutions
Signing domain mismatch: The d= tag in the DKIM signature may not match the From header of the alias domain.
Dedicated DKIM for aliases: Some ESPs allow you to set up separate DKIM records for each alias domain, which is crucial for proper alignment.
Dissecting email authentication headers
When trying to diagnose DMARC failures, the Authentication-Results header is your best friend, but it needs careful reading. It's often separated by semicolons, providing granular details about each authentication check. For example, you might see something like this:
Example Authentication-Results Header
Authentication-Results: spf=pass (sender IP is 2607:f8b0:4864:20::e30)
smtp.mailfrom=alphapixel.com; dkim=fail (no key for signature)
header.d=wildirismarketing.com;dmarc=fail action=oreject
header.from=wildirismarketing.com;compauth=fail reason=000
In this example, SPF passes for alphapixel.com (the smtp.mailfrom domain). However, DKIM explicitly fails with no key for signature, even though the header.d (signing domain) is wildirismarketing.com. The critical part is dmarc=fail and compauth=fail for wildirismarketing.com, indicating that the From domain failed both SPF and DKIM DMARC alignment.
The phrase dkim=fail (no key for signature) in relation to alphapixel.com is misleading here. The problem isn't that alphapixel.com needs a DKIM signature, but that wildirismarketing.com (the From header domain) didn't achieve DMARC alignment through either SPF or DKIM. The action=oreject clearly indicates that the DMARC policy for wildirismarketing.com was set to reject (or quarantine), leading to the rejection.
Troubleshooting strategy and best practices
First, always work with current bounce messages and headers. Old data can be misleading due to policy changes or transient issues. Use tools to check your DMARC reports regularly. If SPF is passing for your primary domain (the smtp.mailfrom), focus on DKIM alignment for your alias domain. Confirm that your alias domain has a proper DKIM record published, and check if your email service provider allows DKIM signing for alias domains with the alias domain itself, not just the primary.
For a robust solution, you might need to configure DKIM specifically for your alias domain, if your provider supports it. If not, consider using a third-party sending service that allows full DKIM control for alias domains, ensuring the d= tag matches your From header domain. Regularly review your DMARC aggregate reports using a platform like Suped to identify any ongoing alignment issues and refine your strategy.
Views from the trenches
Best practices
Validate your DKIM records for alias domains using an online checker to ensure proper syntax and publication.
Use DMARC aggregate reports to quickly identify if DKIM alignment is failing for specific alias domains.
Ensure your email service provider supports separate DKIM configurations for all your alias domains.
Test email authentication with a current bounce message to avoid diagnosing outdated or irrelevant issues.
Common pitfalls
Misinterpreting SPF pass results as DMARC alignment for alias domains due to differing envelope senders.
Assuming a DKIM record's existence means it's being used for alignment, especially with alias domains.
Relying on old email headers for troubleshooting, which might not reflect current authentication policies.
Overlooking the specific 'action=oreject' in Auth-Results headers, indicating a DMARC policy enforcement.
Expert tips
If your provider doesn't support alias DKIM, consider a transactional email service for better control.
Implement a DMARC 'p=none' policy initially to gather reports without impacting email delivery.
Regularly monitor your DMARC reports for insights into authentication outcomes and potential spoofing.
A comprehensive DMARC monitoring tool like Suped can provide clear, actionable recommendations.
Marketer view
Expressed confusion over why DMARC was failing for an alias domain in Google Workspace, especially when DKIM appeared aligned, pointing to a discrepancy in the return-path versus signing domain.
2024-12-16 - Email Geeks
Expert view
Noted that a message rejected by Microsoft would not typically include post-acceptance headers, suggesting a potential misinterpretation of the bounce message or the DMARC policy in effect at the time of the rejection.
2024-12-16 - Email Geeks
Resolving DMARC for alias domains
DMARC failures for alias domains are usually a symptom of alignment issues rather than outright SPF or DKIM validation failures. The discrepancy between the smtp.mailfrom domain and the From header, or the DKIM signing domain's d= tag, is often the culprit. By diligently inspecting email headers and understanding how your email provider handles aliases, you can pinpoint and resolve these issues.
Implementing a robust DMARC monitoring strategy is essential for maintaining strong email authentication. Tools like Suped provide clarity through AI-powered recommendations, real-time alerts, and a unified platform for SPF, DKIM, and DMARC. This ensures that your legitimate emails reach their intended recipients, protecting your brand's reputation and improving deliverability.
Dealing with DMARC failures can be a frustrating experience, especially when you think you've done everything right. It's even more perplexing when you're sending from an alias domain in Google Workspace, and it seems like your DKIM is aligned. I recently encountered a scenario where the DMARC record was failing, despite SPF passing for the return-path domain and a DKIM signature existing for the header domain. This often comes down to a nuanced understanding of DMARC alignment.
