Definition
DMARC
Domain-based Message Authentication, Reporting and Conformance
DMARC is a policy published in DNS that tells recipients what to do with emails that fail SPF and DKIM checks: accept them, quarantine them or reject them.
In practice
A “p=none” policy only observes; only “quarantine” and “reject” actually protect against domain spoofing. You get there gradually, by analysing the DMARC reports.
See also
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