DMARC

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Definition

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an email authentication protocol that builds on SPF and DKIM. It tells receiving servers what to do with emails that fail authentication and provides reports about authentication results.

Why DMARC Matters

DMARC provides the final piece of email authentication by telling receivers exactly what to do with suspicious emails. Without DMARC, receivers make their own decisions about unauthenticated mail. DMARC also provides visibility through reports, letting you see who is sending email using your domain - both legitimate and fraudulent senders.

How DMARC Works

DMARC works by checking that the 'From' domain in an email aligns with either SPF or DKIM authentication. When an email arrives, the receiving server checks SPF and DKIM, then looks up the sender's DMARC policy to determine how to handle failures. DMARC also instructs receivers to send reports back to the domain owner about authentication results.

DMARC Best Practices

Start with p=none to monitor without affecting delivery

Analyze DMARC reports to identify all legitimate senders

Gradually move to p=quarantine, then p=reject

Set up dedicated mailboxes to receive DMARC reports

Ensure SPF and DKIM are properly configured before enforcing DMARC

Frequently Asked Questions

What are DMARC policies?

DMARC has three policy levels: p=none (monitor only), p=quarantine (send failures to spam), and p=reject (block failures entirely). Start with 'none' to gather data, then progress to 'reject' for full protection.

How long does DMARC take to implement?

A full DMARC rollout typically takes 4-12 weeks. This includes setting up monitoring, analyzing reports, fixing authentication issues, and gradually increasing enforcement levels. Rushing can cause legitimate emails to be blocked.