Deliverability and authentication
Whether email reaches the inbox: the DNS records that prove who sent a message, the rules mailbox providers enforce, and the reputation that decides the rest.
DMARC
Email authentication protocol
The DNS policy that ties SPF and DKIM to the From address a reader sees, tells receivers what to do with mail that fails, and asks them to report back. Now RFC 9989.
Coming next in this category: SPF, DKIM, BIMI, ARC, MTA-STS, one-click unsubscribe, and the Gmail, Yahoo and Microsoft sender rules.