Glossary
What is DMARC?
Specifies the policy for messages impersonating a domain based on SPF and DKIM results.
DMARC connects the domain in the visible From header with the domain authenticated by SPF or DKIM. At least one method must both pass and satisfy domain alignment. Publish the policy as TXT under _dmarc, and review real sending sources and reports when introducing it.
Example
_dmarc.example.com. 3600 IN TXT "v=DMARC1; p=none" — This example requests no quarantine or rejection based on DMARC.
Common issue
SPF or DKIM can pass while DMARC fails because the domains are not aligned. p=none does not request rejection of suspicious messages; choose the policy carefully for your actual mail flow.