Defines standard role mailboxes every domain should maintain: postmaster@, abuse@, hostmaster@, etc.

Conceptual overview of the entire internet mail system: MSA, MTA, MDA, MUA roles and their interactions.

Formalises the greylisting technique where MTAs temporarily reject unknown senders to filter out botnet spam.

Defines the Null MX (0 .) record that explicitly signals a domain accepts no incoming mail, preventing delivery loops.

Defines MDN (read receipt) format: the message a mail client sends when a message is read, deleted, or processed.

Previous MDN RFC. Obsoleted by RFC 8098 in 2017.

Defines the Content-Language header for indicating the natural language of message content.

Defines the Content-Disposition header that controls whether attachments are shown inline or as file downloads.

Defines cid: and mid: URI schemes for referencing MIME parts within a message, used in HTML emails with embedded images.

Defines a third-party endorsement mechanism where a trusted voucher certifies a sender's reputation via DNS.