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.
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SPF Record
DNS TXT that lists which mail servers may send email for your domain; subject to a 10-lookup limit.
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DKIM
Digital signatures on outgoing mail, verified with a public key in DNS.
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DMARC
Policy for SPF/DKIM failures plus aggregate reporting (rua).
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DMARC Alignment
Requirement that From: matches SPF or DKIM domain — often breaks with third-party senders.
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PTR Record
Reverse DNS (IP → hostname); critical for inbox delivery.
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Email Spoofing
Forging the From: header; mitigated by SPF, DKIM, and DMARC.
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Subdomain Takeover
Dangling CNAMEs to deprovisioned cloud apps that attackers can reclaim.
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Typosquatting
Lookalike domains for phishing and brand abuse.