Glossary
Alignment
Also called DMARC alignment, identifier alignment.
Last reviewed 18 September 2026
What is DMARC 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.
Mail passes SPF and passes DKIM and fails DMARC when both passes were on the sending provider’s domain while the From line said yours. That is the default state with a good many sending services until the domain setup is finished, and it looks identical to success everywhere except in a DMARC aggregate report.
SPF aligns on the envelope sender, the address bounces are returned to, and DKIM aligns on the domain named in the signature. Only one of the two has to align for DMARC to pass, and relaxed alignment accepts a subdomain of the same organisational domain, which is why sending from a subdomain reserved for mail breaks nothing.
See also
- 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.
- 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.
- Sending domain
A sending domain is the domain that signs and sends your mail, and it is worth separating from the sending infrastructure: the IP addresses mail leaves from are shared by default at every provider serving small senders, while the domain in the signature and the From line is yours alone.
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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