MX record
Specifies which mail servers receive email for a domain. Multiple MX records can be set with priority numbers; lower priority is tried first.
Format
example.com IN MX 10 mail.example.com. routes mail through mail.example.com. A backup at priority 20 takes over if the primary is down.
SPF / DKIM / DMARC
MX gets the mail in; SPF + DKIM + DMARC TXT records prove the sender is authorized. Modern deliverability requires all four configured correctly.