Definition
DMARC (Domain-based Message Authentication, Reporting and Conformance, RFC 7489) is a DNS TXT record published at _dmarc.yourdomain.com. It does two jobs.
First, it sets a policy for mail that fails authentication. The p= tag can be none (just monitor), quarantine (treat as suspicious, usually spam folder) or reject (refuse it).
Second, it adds alignment. A message passes DMARC only if SPF or DKIM passes and the domain that passed matches the domain in the visible From header. Passing SPF for your email platform's bounce domain is not enough on its own.
A minimal record looks like this:
v=DMARC1; p=none; rua=mailto:[email protected]
The rua address receives daily aggregate reports from large mailbox providers, showing which servers sent mail as your domain and whether it passed.
Why it matters
Since February 2024, Gmail and Yahoo require bulk senders to publish a DMARC record, with p=none as the minimum, and to align the From domain with SPF or DKIM. Microsoft set similar requirements for high-volume senders to Outlook.com in 2025. Without DMARC, large volumes of mail from your domain are more likely to be filtered or rejected.
DMARC also protects your domain from spoofing once you move to quarantine or reject. Many teams start at p=none, read reports for a few weeks to find every legitimate sender, fix their SPF and DKIM, then tighten the policy.
How SimpleCold handles it
DMARC describes your sending domain, so it does not affect whether a recipient's address is valid. SimpleCold verifies recipients. For your own records, the free DMARC checker reads your policy and points out common mistakes like a missing record or a malformed tag.