Glossary
Email authentication
Organisational domain
The registrable domain beneath a public suffix — example.co.uk rather than mail.example.co.uk. Relaxed alignment compares organisational domains; strict alignment compares the full names.
Defined in RFC 7489 §3.2.
Where this appears
The lessons that use this term, and what each is for.
Email Authentication FundamentalsWhat alignment meansGiven a message’s three domains, decide whether DMARC will consider it aligned.Email Authentication FundamentalsRelaxed and strictChoose an alignment mode for a domain and defend the choice against its failure cases.SPF PractitionerMoving senders off the apexRestructure an over-budget estate so each platform sends from its own subdomain.SPF PractitionerBrands, regions and acquisitionsDesign SPF for an estate you inherited rather than one you would have built.DMARC Practitionersp and npSet different policies for the apex, existing subdomains and non-existent ones.DMARC PractitionerThe two queriesName the record a receiver applies to any given From domain, and the order it looked.DMARC PractitionerThe Public Suffix ListDerive an organisational domain the way a receiver does, and spot where that goes wrong.DMARC PractitionerWhich half of the estate firstChoose between enforcing the apex and enforcing subdomains first, and defend the order.Email Security PractitionerSequencing an estateOrder an estate of domains so early work makes later work smaller.