RFC 6522: The Multipart/Report Media Type
Defines the multipart/report MIME type used to structure delivery status notifications and other administrative messages.
RFCs
RFC 5965: An Extensible Format for Email Feedback Reports
Defines the ARF (Abuse Reporting Format) used in Feedback Loop (FBL) complaint reports from mailbox providers.
RFC 2142: Mailbox Names for Common Services, Roles and Functions
Defines standard role mailboxes every domain should maintain: postmaster@, abuse@, hostmaster@, etc.
RFC 5598: Internet Mail Architecture
Conceptual overview of the entire internet mail system: MSA, MTA, MDA, MUA roles and their interactions.
RFC 6647: Email Greylisting: An Applicability Statement for SMTP
Formalises the greylisting technique where MTAs temporarily reject unknown senders to filter out botnet spam.
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.
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.