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Senddio glossary · Domain-based Message Authentication, Reporting and Conformance

What is DMARC?

DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email policy standard. It sits on top of SPF and DKIM and tells receiving mail servers exactly what to do when a message claiming to be from your domain fails authentication.

How DMARC works in plain English

You publish a DMARC policy in DNS at _dmarc.yourdomain.com. The policy says one of three things: none (just monitor and report), quarantine (send to spam), or reject (refuse the message entirely). When a receiving server gets a message from your domain, it checks SPF and DKIM, and applies your DMARC policy to the result.

Why DMARC matters

DMARC helps receivers detect unauthorised use of your exact From domain. Receivers apply their own handling policies; DMARC does not prevent display-name abuse, lookalike-domain phishing or all unwanted email.

What does a DMARC record look like?

A DMARC TXT record at _dmarc.yourdomain.com looks like: v=DMARC1; p=reject; rua=mailto:dmarc-reports@yourdomain.com. The p= field is the policy. The rua= field tells receiving servers where to send aggregate failure reports.

Start gentle, then strengthen

Best practice is to start with p=none and monitor reports for a few weeks. Once you confirm that all your legitimate senders are passing SPF and DKIM, move to p=quarantine, then eventually p=reject. Jumping straight to reject can cause legitimate messages to be lost.

Related terms
DKIM SPF
FAQ

DMARC — FAQ

Major receiving providers publish authentication requirements for bulk senders. Check their current sender guidelines rather than assuming one threshold applies to every provider and every message stream.

p=none asks receivers to send you reports but take no action. p=quarantine asks receivers to deliver failing messages to spam. p=reject asks receivers to refuse failing messages outright. Most mature domains run on p=reject after a careful rollout.

The domain setup shows a suggested DMARC record to publish in your DNS. You control the policy and should review authentication reports before moving to quarantine or reject.

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