Email RFC Reference
The complete guide to every RFC that powers internet email. SMTP, DKIM, SPF, DMARC, MIME, TLS, and more — explained for developers.
Core SMTP & Message Format
RFC 1869 SMTP Service Extensions (ESMTP)
RFC 2920 SMTP Pipelining
RFC 3030 SMTP BINARYMIME and CHUNKING
RFC 5321 Simple Mail Transfer Protocol
RFC 5322 Internet Message Format
RFC 5598 Internet Mail Architecture
RFC 6409 Message Submission for Mail
RFC 6531 SMTP Extension for Internationalized Email
RFC 6532 Internationalized Email Headers
Email Authentication
RFC 4954 RFC 4954: SMTP AUTH Extension
RFC 5617 Author Domain Signing Practices
RFC 8463 RFC 8463: Ed25519 for DKIM Signatures
RFC 8601 Authentication-Results Header Field
RFC 8617 Authenticated Received Chain
RFC 6376 DomainKeys Identified Mail
RFC 7489 Domain-based Message Authentication, Reporting and Conformance
RFC 7208 Sender Policy Framework
Transport Security
RFC 3207 SMTP STARTTLS Extension
RFC 7817 RFC 7817: Updated TLS Server Identity Check for Email
RFC 8314 RFC 8314: Cleartext Considered Obsolete
RFC 8689 RFC 8689: SMTP Require TLS Option
RFC 7672 DNS-Based Authentication for SMTP TLS
RFC 8461 Mail Transfer Agent Strict Transport Security
MIME — Multipurpose Internet Mail Extensions
RFC 2045 Format of Internet Message Bodies
RFC 2046 Media Types
RFC 2047 Message Header Extensions for Non-ASCII Text
RFC 2049 Conformance Criteria and Examples
RFC 2231 RFC 2231: MIME Parameter Value Extensions
Delivery Status & Bounce Handling
RFC 3461 RFC 3461: SMTP Delivery Status Notification Extension
RFC 3462 RFC 3462: Multipart/Report Content Type
RFC 3463 RFC 3463: Enhanced Mail System Status Codes
RFC 3464 RFC 3464: Delivery Status Notification Format
RFC 5248 RFC 5248: SMTP Enhanced Status Codes Registry
RFC 6522 RFC 6522: Multipart/Report Media Type (Updated)
Abuse Reporting & Feedback
RFC 5965 Abuse Reporting Format
RFC 6591 RFC 6591: Authentication Failure Reporting (AFRF)
RFC 6652 RFC 6652: SPF Authentication Failure Reporting
RFC 8460 RFC 8460: SMTP TLS Reporting (TLSRPT)
Mailing Lists & Header Fields
RFC 2369 RFC 2369: List-Unsubscribe and List-* Headers
RFC 3834 RFC 3834: Automatic Responses in Email
RFC 6377 RFC 6377: DKIM and Mailing Lists
RFC 6854 RFC 6854: Group Syntax in From and Sender Header Fields
RFC 8058 RFC 8058: One-Click Unsubscribe for Email
DNS & Mail Routing
RFC 1035 Domain Names: Implementation and Specification
RFC 5782 RFC 5782: DNS-Based Blacklists and Whitelists
RFC 6186 RFC 6186: SRV Records for Email Service Autodiscovery
RFC 7505 No Service for Domain
Mail Access Protocols
RFC 1939 Post Office Protocol Version 3
RFC 8620 JSON Meta Application Protocol
RFC 9051 RFC 9051: IMAP4rev2
Content Security
RFC 5751 RFC 5751: S/MIME 3.2 Message Specification
RFC 8551 RFC 8551: S/MIME 4.0 Message Specification
Email Concepts Encyclopedia
Guide Anatomy of Email Headers
Guide DNS and Mail Routing
Guide Email Authentication Explained
Guide How SMTP Really Works
Guide How Spam Filters Work
Guide IP and Domain Reputation
Guide TLS and Email Security
Guide The Complete Email Deliverability Guide
Guide The Lifecycle of an Email
Guide Understanding Email Bounces