Mail and DNS standards are published by the Internet Engineering Task Force in its RFC document series. Here are some of the more important RFCs. For a longer list see UASG 006,
For SMTP
- RFC 5321 – Simple Mail Transfer protocol, from one MTA to another (previously RFCs 821 and 2821)
- RFC 6609 – Mail submission, from MUA to MSA (previously RFCs 2476 and 4409)
For mail message formats
- RFC 5322 – Internet Message Format (previously RFCs 822 and 2822)
- 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 – MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
- RFC 2048 – Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures
- RFC 2049 – Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples
- RFC 3464 – An Extensible Message Format for Delivery Status Notifications
- RFC 6854 – Update to Internet Message Format to Allow Group Syntax in the “From:” and “Sender:” Header Fields
For POP and IMAP
- RFC 1939 – Post Office Protocol – Version 3 (POP3)
- RFC 3501 – Internet Message Access Protocol – Version 4rev1 (IMAP4)
For IDNs
- RFC 3629: UTF-8, a transformation format of ISO 10646
- RFCs 5890, 5891, 5892, 5893, 5894, and 5895 – Internationalized Domain Names for Applications (IDNA)
For EAI mail
- RFC 6530 – Overview and Framework for Internationalized Email
- RFC 6531 – SMTP Extension for Internationalized Email
- RFC 6532 – Internationalized Email Headers
- RFC 6533 – Internationalized Delivery Status and Disposition Notifications
- RFC 6855 – IMAP Support for UTF8
- RFC 6856 – Post Office Protocol Version 3 (POP3) Support for UTF-8
- RFC 6857 – Post-Delivery Message Downgrading for Internationalized Email Messages
- RFC 6858 – Simplified POP and IMAP Downgrading for Internationalized Email
For PRECIS and string mapping
- RFC 8264 – PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols
- RFC 8265 – Preparation, Enforcement, and Comparison of Internationalized Strings Representing Usernames and Passwords
- RFC 8266 – Preparation, Enforcement, and Comparison of Internationalized Strings Representing Nicknames
- RFC 7790 – Mapping Characters for Classes of the Preparation, Enforcement, and Comparison of Internationalized Strings (PRECIS)
- RFC 6885 – Stringprep Revision and Problem Statement for the Preparation and Comparison of Internationalized Strings (PRECIS)
- RFC 6943 – Issues in Identifier Comparison for Security Purposes
For SASL
These define the methods for logging in and authenticating for POP, IMAP, and submission, using UTF-8 usernames and passwords.
- RFC 4422 – Simple Authentication and Security Layer (SASL)
- RFC 4616 – The PLAIN Simple Authentication and Security Layer (SASL) Mechanism
- The LOGIN SASL Mechanism Internet draft
- IANA SASL methods registry