DMARC
DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol that builds on [[spf-record|SPF]] and [[dkim|DKIM]]. It tells receiving mail servers what to do when messages fail authentication and provides reporting on email abuse.
Example
A DMARC policy of 'v=DMARC1; p=reject' instructs receiving servers to reject any email claiming to be from your domain that fails SPF/DKIM checks.
Referenced in Guides
DNS Configuration