Understanding DMARC failures

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a protocol that tells receiving mail servers how to handle messages that fail authentication. When a message doesn’t pass SPF or DKIM alignment, DMARC can instruct the provider to deliver it to the inbox, send it to spam, quarantine it, or reject it outright.

Common questions and concise answers

1. What does a DMARC failure mean for my email?

It means the message didn’t pass the domain’s authentication checks. The receiving server will follow the DMARC policy you set – it might still deliver the mail, drop it into spam, or reject it entirely. This protects your brand from spoofing but can also block legitimate traffic if SPF or DKIM aren’t aligned.

2. Why do DMARC failures happen?

They usually stem from mis‑aligned SPF or DKIM records. If a sending service isn’t listed in your SPF record or its DKIM signature doesn’t match the From domain, the message fails DMARC. Common culprits are third‑party platforms, forwarding services, and outdated DNS entries.

3. Which email providers reject messages because of DMARC?

Major providers such as Gmail, Outlook, and Yahoo enforce DMARC policies. Their bounce messages often contain codes like “550‑5.7.26” (Gmail) or “550 5.7.509” (Outlook) indicating a DMARC‑related rejection.

4. How does my DMARC policy affect delivery?

Your policy (p=none, p=quarantine, or p=reject) tells receivers what to do with failing messages. “none” only reports failures, “quarantine” moves them to spam, and “reject” blocks them at the gateway. Gradually tightening the policy helps you catch issues before you go full‑reject.

5. What are the most common causes of DMARC failures?

Typical causes include email forwarding, mis‑configured third‑party senders, subdomain alignment gaps, expired DKIM keys, and multiple SPF records. Each of these breaks the alignment checks that DMARC relies on.

6. How can email forwarding break DMARC?

Forwarding often changes the envelope‑from address, breaking SPF alignment. DKIM may survive, but any header tweaks can invalidate the signature. Using relaxed alignment or ARC can mitigate the issue.

7. Why do third‑party services cause DMARC fails?

Platforms like Mailchimp, Salesforce, or payroll tools send on your behalf but may not be authorized in your SPF record. If they don’t publish a DKIM signature that aligns with your domain, their messages will fail DMARC.

8. How do subdomains impact DMARC alignment?

DMARC checks the exact domain in the From address. If you send from mail.example.com but only have a policy for example.com, the subdomain can fail unless you publish a separate DMARC record or use the sp= tag.

9. What problems arise from missing or expired DKIM keys?

DKIM signatures rely on a public key stored in DNS. If the key is removed, rotated incorrectly, or expires, the signature can’t be verified, causing a DMARC fail.

10. Why can multiple SPF records cause DMARC failures?

SPF requires a single TXT record per domain. Having two records (e.g., one for Google Workspace and another for a marketing cloud) makes the SPF check invalid, which in turn forces DMARC to fail.

11. How can I test whether my DMARC is failing?

Start by reviewing aggregate reports sent to the RUA address in your DMARC record. Then use online tools like Palisade’s DMARC score checker to validate your DNS records. Finally, send test emails to Gmail, Outlook, and Yahoo and inspect the Authentication-Results header.

12. What steps should I take to fix DMARC failures?

Follow a systematic checklist:

• Gather DMARC reports to identify failing sources.
• Ensure every legitimate sender (ESP, CRM, helpdesk) is included in your SPF record.
• Enable DKIM signing for each platform and verify alignment.
• Consolidate SPF into a single record.
• Test changes with real‑world email sends and monitor the reports.

When you’re confident all services are authenticated, move your policy from p=none → p=quarantine → p=reject for maximum protection.

Quick Takeaways

• DMARC failures indicate mis‑aligned SPF or DKIM.
• Common culprits: forwarding, third‑party senders, subdomains, expired DKIM keys, multiple SPF records.
• Major providers (Gmail, Outlook, Yahoo) will reject or spam‑filter failing messages.
• Start with p=none, monitor reports, then tighten to p=quarantine and finally p=reject.
• Use Palisade’s free tools to check DMARC, SPF, DKIM, and BIMI health: DMARC score, SPF checker, DKIM validator, BIMI status.
• Regularly audit DNS records and update keys before they expire.

Frequently Asked Questions

• Do I need to set DMARC to p=reject? Not immediately. Begin with p=none to collect data, then progress to p=quarantine and finally p=reject once all senders are authenticated.
• Can I use ARC to fix forwarding issues? Yes, Authenticated Received Chain (ARC) preserves authentication results across forwarders, helping SPF‑based failures.
• What is the difference between SPF and DKIM alignment? SPF aligns the sending IP with the envelope‑from domain, while DKIM aligns the cryptographic signature’s domain with the visible From address.
• How often should I rotate DKIM keys? Rotate annually or whenever you suspect a key compromise; always update the DNS record promptly.
• Is a single DMARC record enough for subdomains? Use the sp= tag to apply the same policy to subdomains, or publish separate DMARC records for each subdomain.

Ready to get a clear view of your email authentication health? Check your DMARC score now and start fixing failures today.