RFC 7505: A Null MX No Service Resource Record for Domains That Accept No Mail
Defines the Null MX (0 .) record that explicitly signals a domain accepts no incoming mail, preventing delivery loops.
Standards & Protocols
RFC 8098: Message Disposition Notification
Defines MDN (read receipt) format: the message a mail client sends when a message is read, deleted, or processed.
RFC 3798: Message Disposition Notification
Previous MDN RFC. Obsoleted by RFC 8098 in 2017.
RFC 3282: Content Language Headers
Defines the Content-Language header for indicating the natural language of message content.
RFC 2183: Communicating Presentation Information in Internet Messages
Defines the Content-Disposition header that controls whether attachments are shown inline or as file downloads.
RFC 2392: Content-ID and Message-ID Uniform Resource Locators
Defines cid: and mid: URI schemes for referencing MIME parts within a message, used in HTML emails with embedded images.
RFC 5518: Vouch By Reference (VBR)
Defines a third-party endorsement mechanism where a trusted voucher certifies a sender's reputation via DNS.
RFC 5863: DomainKeys Identified Mail (DKIM) Development, Deployment, and Operations
Operational guide for deploying DKIM: key rotation, selector management, DNS setup, and troubleshooting.
RFC 8601: Message Header Field for Indicating Message Authentication Status
Defines the Authentication-Results header that records SPF, DKIM, and DMARC check outcomes for downstream processing and BIMI.
RFC 1847: Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted
Defines MIME framework for signed and encrypted message parts, foundation for S/MIME and PGP/MIME.
RFC 5751: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2
Defines S/MIME 3.2 for signing and encrypting email using X.509 certificates.
RFC 1939: Post Office Protocol Version 3 (POP3)
Defines the POP3 protocol for downloading email from a server to a local client.
