Glossary

DNS & email security terms

Short definitions for SPF, DKIM, DMARC, and related concepts. Each entry links to the DomainPreflight tool that helps you verify or fix the issue.

• SPF Record

  DNS TXT that lists which mail servers may send email for your domain; subject to a 10-lookup limit.

• DKIM

  Digital signatures on outgoing mail, verified with a public key in DNS.

• DMARC

  Policy for SPF/DKIM failures plus aggregate reporting (rua).

• DMARC Alignment

  Requirement that From: matches SPF or DKIM domain — often breaks with third-party senders.

• PTR Record

  Reverse DNS (IP → hostname); critical for inbox delivery.

• Email Spoofing

  Forging the From: header; mitigated by SPF, DKIM, and DMARC.

• Subdomain Takeover

  Dangling CNAMEs to deprovisioned cloud apps that attackers can reclaim.

• Typosquatting

  Lookalike domains for phishing and brand abuse.