RFC List

General RFCs

RFC 822: Mail Message Format
RFC 1123: Requirements for Internet Hosts -- Application and Support (updated by RFC 2821)
RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
RFC 2822: Internet Message Format

SMTP RFCs

RFC 821: SMTP Protocol
RFC 974: Mail Routing and the Domain System
RFC 1652: SMTP Service Extension for 8bit-MIMEtransport (elective, but widely adopted)
RFC 1830: SMTP Service Extensions for Transmission of Large and Binary MIME Messages (experimental, but cool idea)
RFC 1869: SMTP Service Extensions
RFC 1870: SMTP Service Extension for Message Size Declaration
RFC 1891: SMTP Service Extension for Delivery Status Notifications (elective)
RFC 1893: Enhanced Mail System Status Codes (experimental)
RFC 1985: SMTP Service Extension for Remote Message Queue Starting (elective)
RFC 2034: SMTP Service Extension for Returning Enhanced Error Codes (elective)
RFC 2142: Mailbox Names For Common Services, Roles And Functions
RFC 2197: SMTP Service Extension for Command Pipelining (elective)
RFC 2554: SMTP Service Extension for Authentication
RFC 2821: Simple Mail Transfer Protocol (obsoletes RFC 821)
RFC 6710: Simple Mail Transfer Protocol Extension for Message Transfer Priorities

LMTP RFCs

RFC 2033 : LMTP Local Mail Transfer Protocol

JMAP standard

JMAP specifications

IMAP RFCs

RFC 1731: IMAP4 Authentication Mechanisms
RFC 2060: IMAP Version 4rev1
RFC 2086: IMAP4 ACL extension
RFC 2087: IMAP4 QUOTA extension
RFC 2088: IMAP4 non-synchronizing literals
RFC 2177: IMAP4 IDLE command
RFC 2180: IMAP4 Multi-accessed Mailbox Practice
RFC 2192: IMAP URL Scheme
RFC 2193: IMAP4 Mailbox Referrals
RFC 2195: IMAP/POP AUTHorize Extension for Simple Challenge/Response
RFC 2221: IMAP4 Login Referrals
RFC 2342: IMAP4 Namespace (elective)
RFC 2359: IMAP4 UIDPLUS extension (elective)
RFC 2595: Using TLS with IMAP, POP and ACAP
RFC 2683: IMAP4 Implementation Recommendations
RFC 5256: IMAP4 SORT and THREAD Extensions
RFC 5464: IMAP METADATA Extension

ManageSieve RFC

RFC 5804: A Protocol for Remotely Managing Sieve Scripts

Sieve RFCs

RFC 5228: Sieve: An Email Filtering Language RFC 2298: Extensible Message Format for Message Disposition Notifications RFC 5173: Sieve Email Filtering: Body Extension RFC 5230: Sieve Email Filtering: Vacation Extension

POP3 RFCs

RFC 1725: POP3 Protocol
RFC 1734: POP3 AUTHentication command
RFC 1939: POP3 Protocol (obsoletes RFC 1725)

NNTP RFCs (v 2.3.x only)

RFC 977: NNTP Protocol
RFC 1036: Format of News Messages
RFC 2980: Common NNTP Extensions
NNTP Working Group