DNS
DNS concepts for email
Record types and behaviors that matter for sending and receiving mail — linked guides as they are published.
A and AAAA records
Hostnames to IPv4 and IPv6 for mail servers.
CNAME records
Aliases, apex limitations, and takeovers.
MX records
Priority, fallback, and receiving mail.
TXT records
SPF, DKIM, DMARC, and string length limits.
NS delegation
Who answers queries for your zone.
PTR and reverse DNS
IP to hostname for outbound reputation.