This page contans a list of relevent IETF standards that concern the tranmission and handing of email messages.

• RFC1524, A User Agent Configuration Mechanism For Multimedia Mail Format Information.
• RFC1939, Post Office Protocol - Version 3.
• RFC2045, Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies.
• RFC2046, Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types.
• RFC2047, MIME (Multipurpose * Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text.
• RFC2087. IMAP Quota Extension
• RFC2156, MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME
• RFC2177, IMAP IDLE Command
• RFC2183, Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field.
• RFC2279, UTF-8, a transformation format of ISO 10646.
• RFC2231, MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations.
• RFC2369, The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields.
• RFC2822, Internet Message Format
• RFC3156, MIME Security with OpenPGP.
• RFC3501, IMAP (Internet Message Access Protocol) - Version 4rev1
• RFC3676, The Text/Plain? Format and DelSp? Parameters (a.k.a Format=Flowed).
• RFC4314, IMAP4 Access Control List (ACL) Extension
• RFC4466, Collected Extensions to IMAP4 ABNF
•  The Maildir format
•  Maildir++

A more complete list can be found at:  http://www.tin.org/docs.html.