STANDARDS

Email standards map

Email is a stack of standards accumulated over decades. This map points to the parts most operators encounter. For a larger catalog, see the RFC index and RFC map.

Core message and transport

RFC 5321 defines SMTP transport. RFC 5322 defines Internet Message Format. RFC 6409 covers message submission. Start with SMTP and message format.

Message bodies and attachments

The MIME family defines media types, multipart bodies, transfer encodings, and non-ASCII content. See MIME, Content-Type, and Content-Transfer-Encoding.

Authentication

RFC 7208 defines SPF. RFC 6376 defines DKIM. DMARC's current standards-track specification is covered in the current DMARC standard. See also email authentication.

Transport security

RFC 3207 defines SMTP STARTTLS, RFC 8461 defines MTA-STS, RFC 8460 defines TLS-RPT, and RFC 7672 defines SMTP security using DANE. See STARTTLS, MTA-STS, TLS-RPT, and DANE.

Delivery status and feedback

Enhanced status codes and DSNs make delivery failures machine-readable; feedback-report formats support abuse reporting. See enhanced status codes, DSN, and ARF.

Lists and unsubscribe

List headers and one-click unsubscribe have their own standards and operational requirements. See List-* headers and one-click unsubscribe.

Reading standards safely

An RFC number alone does not tell you whether a document is current, updated, experimental, informational, or superseded. Check the RFC Editor record and errata before treating an older document as the final word.