- RFC 1847 Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted
- RFC 2045 Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
- RFC 2046 Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
- RFC 2047 Multipurpose Internet Mail Extensions (MIME) Part Three: Message Header Extensions for Non-ASCII Text
- RFC 2049 Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples
- RFC 2076 Common Internet Message Headers
- RFC 2183 Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field
- RFC 2231 MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations
- RFC 2387 The MIME Multipart/Related Content-type
- RFC 3030 SMTP Service Extensions for Transmission of Large and Binary MIME Messages
- RFC 3156 MIME Security with OpenPGP
- RFC 3676 The Text/Plain Format and DelSp Parameters
- RFC 3798 Message Disposition Notification
- RFC 3801 Voice Profile for Internet Mail - version 2 (VPIMv2)
- RFC 3864 Registration Procedures for Message Header Fields
- RFC 4021 Registration of Mail and MIME Header Fields
- RFC 4289 Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures
- RFC 5321 Simple Mail Transfer Protocol
- RFC 5322 Internet Message Format
- RFC 6152 SMTP Service Extension for 8-bit MIME Transport
- RFC 6376 DomainKeys Identified Mail (DKIM) Signatures
- RFC 6409 Message Submission for Mail
- RFC 6530 Overview and Framework for Internationalized Email
- RFC 6531 SMTP Extension for Internationalized Email
- RFC 6532 Internationalized Email Headers
- RFC 6657 Update to MIME regarding "charset" Parameter Handling in Textual Media Types
- RFC 6838 Media Type Specifications and Registration Procedures (best practices, related?)
- RFC 6854 Update to Internet Message Format to Allow Group Syntax in the "From:" and "Sender:" Header Fields
Message Tracking
- RFC 3885 SMTP Service Extension for Message Tracking
- RFC 3886 An Extensible Message Format for Message Tracking Responses
- RFC 3887 Message Tracking Query Protocol
- RFC 3888 Message Tracking Model and Requirements
IMAP
- RFC 3501 INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
- RFC 4466 Collected Extensions to IMAP4 ABNF
- RFC 4551 IMAP Extension for Conditional STORE Operation or Quick Flag Changes Resynchronization
- RFC 5032 WITHIN Search Extension to the IMAP Protocol
- RFC 5182 IMAP Extension for Referencing the Last SEARCH Result
- RFC 5738 IMAP Support for UTF-8