Cybersecurity & Email Authentication Glossary
Authoritative technical definitions and RFC specifications for email authentication, transport encryption, anti-spoofing protocols, and modern web threat detection.
Sender Policy Framework (SPF)
A DNS-based email validation system designed to prevent email spoofing by allowing domain owners to specify which IP addresses and mail servers are authorized to send email on behalf of their domain.
DomainKeys Identified Mail (DKIM)
An asymmetric cryptographic authentication standard that allows organizations to sign outbound email headers and bodies with a private key, verified by recipients using a public key published in DNS.
Domain-based Message Authentication, Reporting & Conformance (DMARC)
A policy framework that builds upon SPF and DKIM to enforce identifier alignment between the visual From: header and authentication results, with options for monitoring (p=none), quarantine, or strict rejection.
Brand Indicators for Message Identification (BIMI)
An email standard that allows DMARC-enforced domain owners to display their official trademarked brand logo alongside authenticated emails in recipient inboxes such as Gmail, Apple Mail, and Yahoo.
Mail Transfer Agent Strict Transport Security (MTA-STS)
A security mechanism that allows domains to declare their ability to receive TLS-encrypted SMTP connections and mandate that sending servers fail delivery if TLS cannot be negotiated securely.
SMTP TLS Reporting (TLS-RPT)
A reporting standard that enables receiving domains to collect aggregate telemetry regarding TLS connection failures and MTA-STS policy validation issues experienced by sending mail transfer agents.
Authenticated Received Chain (ARC)
An email authentication protocol designed to preserve SPF and DKIM verification results when messages traverse intermediate forwarders, mailing lists, and multi-hop relays.
Verified Mark Certificate (VMC)
A digital certificate issued by an authorized Certificate Authority (DigiCert or Entrust) confirming legal ownership of a registered trademark logo required for BIMI display in major mailboxes.
IDN Homograph Attack
A visual impersonation technique where attackers register internationalized domain names using lookalike Unicode characters (e.g. Cyrillic "а" instead of Latin "a") to spoof legitimate brand domains.
Shannon Entropy
A mathematical measure of randomness within a character string. High Shannon entropy in domain names often indicates algorithmically generated domain names (DGA) or obfuscated malware staging URLs.
Quishing (QR Code Phishing)
A social engineering attack where malicious URLs are encoded inside QR codes on physical posters, PDF invoices, or emails to bypass corporate link scanners and trick mobile users into credential harvesting traps.
Typosquatting (URL Hijacking)
The malicious registration of commonly misspelled variants of popular domain names (e.g. gogle.com or paypa1.com) to intercept accidental mistyped traffic and deliver malware or phishing pages.
DNS-over-HTTPS (DoH)
A protocol for performing remote Domain Name System resolution via encrypted HTTPS transactions to prevent eavesdropping, DNS spoofing, and man-in-the-middle manipulation.
Transport Layer Security (TLS 1.3)
The modern cryptographic protocol that provides end-to-end communications security over the Internet, featuring zero-round-trip (0-RTT) handshakes and mandatory forward secrecy.
Registration Data Access Protocol (RDAP)
The modern RESTful JSON-based successor to legacy WHOIS, providing standardized, structured access to domain name registration and registrar ownership metadata.