Glossary
DMARC
Also called Domain-based Message Authentication, Reporting and Conformance.
Last reviewed 18 September 2026
What is DMARC?
DMARC is the DNS policy that ties SPF and DKIM to the domain a reader actually sees, telling receivers what to do with mail from your domain that aligns with neither and asking for aggregate reports about it, and it is defined in RFC 7489.
The record lives at _dmarc under your domain, and its policy tag is the point of it: none means report what is happening and deliver it anyway, quarantine means treat failures as suspicious, and reject means refuse them. A domain that sends no mail at all should publish a reject policy, which is the cheapest anti-impersonation measure available to anybody who owns a domain.
A policy of none is the right place to start and the wrong place to stay. Its purpose is to collect aggregate reports for a few weeks so you can find the legitimate senders you had forgotten about and fix their authentication; a domain that has been on none for three years has a record that satisfies the bulk sender requirement and has never once caused a forged message to be refused.
See also
- SPF
SPF is a DNS record listing the servers allowed to send mail for a domain, checked by the receiver against the envelope sender rather than against the From line a reader sees, and it is defined in RFC 7208.
- DKIM
DKIM is a cryptographic signature over a message’s headers and body, made with a private key held by whoever sends the mail and checked by the receiver against a public key published in DNS under a selector, and it is defined in RFC 6376.
- Alignment
Alignment is the DMARC requirement that the domain a reader sees in the From header match a domain that passed SPF or DKIM, which is why a message can pass both of those checks and still fail DMARC.
- Bulk sender requirements
The bulk sender requirements are the list Google and Yahoo both began enforcing in February 2024: SPF and DKIM on the sending domain, a DMARC record on the From domain, one-click unsubscribe in the headers, unsubscribe requests honoured within two days, and a spam complaint rate under 0.3 per cent.
Read next
This term is covered properly in How to set up SPF, DKIM and DMARC for a sending domain, which is a longer piece on the subject.
Every other term is on the glossary index , the longer writing is in the guides, and what this site itself does is on the home page.
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