Email & DNS Glossary
Understanding email security and DNS starts with knowing the terminology. This glossary covers the key terms you will encounter when configuring, troubleshooting, and securing your domain's email infrastructure.
SPF
Sender Policy Framework — a DNS record that specifies which mail servers are authorized to send email for your domain.
DKIM
DomainKeys Identified Mail — a cryptographic email authentication method that verifies message integrity using digital signatures.
DMARC
Domain-based Message Authentication, Reporting & Conformance — a policy that tells receivers how to handle emails failing SPF or DKIM.
MX Record
A DNS record that specifies the mail servers responsible for receiving email on behalf of a domain.
DNS
Domain Name System — the internet's phone book that translates human-readable domain names into IP addresses.
SSL/TLS
Secure Sockets Layer / Transport Layer Security — cryptographic protocols that encrypt data in transit between clients and servers.
WHOIS
A protocol and database for querying domain registration information, including registrant details and name servers.
TXT Record
A DNS record type used to store text-based information, commonly used for SPF, DKIM, DMARC, and domain verification.
Email Blacklist
A real-time database (DNSBL) that lists IP addresses or domains known to send spam or malicious email.
PTR Record
A DNS record used for reverse DNS lookups, mapping an IP address back to a hostname for sender verification.
SMTP
Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages across the internet.
IMAP
Internet Message Access Protocol — an email retrieval protocol that syncs messages across multiple devices by keeping them on the server.
POP3
Post Office Protocol v3 — an email retrieval protocol that downloads messages to a single device, typically removing them from the server.
BIMI
Brand Indicators for Message Identification — an email standard that displays your brand logo next to authenticated emails in the inbox.
MTA-STS
Mail Transfer Agent Strict Transport Security — a standard that enforces TLS encryption for inbound email, preventing downgrade attacks.
CNAME Record
A DNS record that maps one hostname to another (an alias), commonly used for subdomains, CDNs, and SaaS integrations.
A Record
The most fundamental DNS record type, mapping a domain name or hostname directly to an IPv4 address.
NS Record
A DNS record that specifies which nameservers are authoritative for a domain, delegating DNS resolution.
Reverse DNS
The process of resolving an IP address back to a hostname using PTR records, critical for email deliverability and spam prevention.
Email Bounce
A delivery failure notification (hard or soft) returned when an email cannot be delivered, impacting sender reputation.