DMARC

The policy that tells receivers what to do when mail fails SPF and DKIM, and where to report.

DMARC ties SPF and DKIM to the visible From address. The policy is none (monitor), quarantine (spam folder) or reject. Daily aggregate reports to the rua address show every service sending as you, which is how forgotten senders surface before you enforce. Gmail and Yahoo require DMARC from bulk senders since 2024.

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SPF (Sender Policy Framework): A DNS record listing which servers may send email for your domain.
DKIM (DomainKeys Identified Mail): A signature on each message, checked against a public key in your DNS.
BIMI: Your logo next to your messages in supporting inboxes, once DMARC is enforced.

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