DMARC
A DNS-published policy layer built on SPF and DKIM, through which a domain owner states how receivers should handle messages that fail authentication, and where reports should be sent.
In plain terms
The instruction that ties SPF and DKIM together and tells receivers what to do when they fail.
Why it matters for deliverability
SPF and DKIM alone tell a receiver whether a check passed. DMARC is what tells them what that should mean, and it is now a baseline requirement for bulk senders at the major mailbox providers.
What to do about it
- Publish a record at p=none first and read the aggregate reports before changing anything.
- Fix alignment for every legitimate source you find in those reports.
- Only then move to quarantine, and later reject.
Source
RFC 7489 — Domain-based Message Authentication, Reporting, and Conformance (DMARC)
“a scalable mechanism by which a mail-originating organization can express domain-level policies and preferences for message validation, disposition, and reporting”
Checked 2026-08-29
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Definitions reviewed 2026-08-29. Spotted something wrong? Tell us.
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