What is the most common cause of a DMARC failure?

The most common reasons messages fail DMARC. The most common cause is misaligned DKIM signatures. When a service like G Suite signs mail with its own domain (e.g., d=example.gappssmtp.com) instead of your domain, DMARC sees the signature as unauthenticated and flags the message.

How does SPF affect DMARC alignment?

SPF checks the envelope sender IP against authorized hosts. If the SPF record does not include the sending service, DMARC treats the message as unauthenticated, even if DKIM passes. Ensure all legitimate outbound IPs are listed in your SPF record.

Why do third‑party marketing platforms break DMARC?

Platforms like SendGrid or MailChimp send mail on your behalf but use their own DKIM domains. Without adding the provider’s SPF include and DKIM public key to your DNS, the messages fail alignment and DMARC reports them as failures.

What steps should I take after seeing DMARC failures in my reports?

Start by enabling DMARC monitoring (p=none) to collect data without affecting delivery. Review the aggregate reports to identify which sources are failing, then add or correct SPF/DKIM records for those sources. Once alignment is achieved, gradually move to a stricter policy (p=quarantine, then p=reject). The rollout path from p=none monitoring to full p=reject enforcement.

How do I verify that my DKIM keys are correctly configured?

Use Palisade’s DKIM signing tool to test your selector and public key. The tool will confirm that the DNS record is reachable and that the signature matches the expected value.

What is the role of BIMI in DMARC compliance?

BIMI builds on DMARC to display your brand logo in supporting inboxes. It requires a DMARC policy of at least quarantine. Verify your BIMI setup with Palisade’s BIMI verification tool.

How can I check my SPF record for syntax errors?

Run Palisade’s SPF record checker. It will highlight missing mechanisms, too many DNS lookups, or syntax mistakes that could cause DMARC failures.

Is there a single dashboard to view all DMARC activity?

Yes. Palisade provides an email security score dashboard that aggregates DMARC, SPF, DKIM, and BIMI data in one place, making troubleshooting faster.

Why DMARC Fails and How to Fix It

By Samuel ChenardSeptember 30, 2025Updated August 5, 20265 min read

Why Does DMARC Fail and How Can You Fix It?

DMARC failures can leave your organization vulnerable to phishing and spoofing attacks — and, just as often, they quietly send your own legitimate mail to spam. A DMARC "failure" simply means a message did not pass an aligned SPF or DKIM check for the domain in the From: header. Understanding why that happens is the first step toward a robust email security posture, and to safely reaching an enforcement policy without blocking real mail.

At a glance

Quick Takeaways

DMARC relies on SPF and DKIM alignment to verify senders.
Misconfigured DKIM signatures from G Suite or Office 365 cause failures.
Third‑party senders (SendGrid, MailChimp, etc.) need proper SPF/DKIM records.
Header tampering or unauthorized sources break DKIM authentication.
Enable DMARC monitoring (p=none) before enforcing stricter policies.
Identify all legitimate mail sources and whitelist them.
Gradually raise your DMARC policy to reject or quarantine suspicious mail.

Frequently Asked Questions

What does “alignment” mean in DMARC? Alignment means the domain in the SPF or DKIM check matches the domain in the From: header. Without alignment, DMARC treats the message as unauthenticated.
Can I use multiple DKIM selectors? Yes. Multiple selectors let you rotate keys without downtime. Just ensure each selector’s public key is published in DNS.
Do I need a separate DMARC record for each subdomain? Only if you want different policies. Otherwise, a top‑level DMARC record with “sp=none” will apply to subdomains.
How often should I review my DMARC reports? At least weekly during the monitoring phase, then monthly once enforcement is stable.
What is the impact of a “p=reject” policy? Legitimate mail that fails alignment will be blocked by receiving servers, reducing phishing risk but potentially causing delivery issues if your records are incomplete.

By following these steps and using Palisade’s suite of email authentication tools, you can turn DMARC failures into a proactive security advantage.

Questions readers ask

Common Questions About DMARC Failures

Yes. Forwarding services often modify the message header or rewrite the body, breaking the DKIM signature, and the forwarder's IP will not be in your SPF record, so SPF fails too. If the forwarder does not preserve SPF alignment, DMARC will fail on both counts. ARC (Authenticated Received Chain) lets a trusted forwarder vouch that the message passed authentication before it altered anything, which receivers can honor — but ARC is only useful when the receiving side chooses to trust the forwarder, so it is not a universal fix. Where you control the flow, prefer re-sending over forwarding, or send from a subdomain dedicated to the forwarding path.

After you have identified and whitelisted all legitimate sources, and your aggregate reports show < 5% failure rate, you can shift to p=quarantine. A common mistake is enforcing too early, while a real sending service is still failing alignment — that blocks your own mail. Monitor the impact for a week or two, watching for any legitimate source that suddenly drops, then move to p=reject for maximum protection once the reports stay clean.