RFC 2919: List-Id: A Structured Field and Namespace for the Identification of Mailing Lists
Defines the List-Id header for uniquely identifying mailing lists, used by email clients to organise list mail.
RFCs
RFC 6530: Overview and Framework for Internationalized Email
Framework RFC for EAI (Email Address Internationalization) supporting Unicode email addresses and headers.
RFC 6531: SMTP Extension for Internationalized Email
Defines the SMTPUTF8 SMTP extension that allows UTF-8 in MAIL FROM, RCPT TO, and headers.
RFC 6532: Internationalized Email Headers
Defines UTF-8 encoded headers for internationalized email messages.
RFC 5890: Internationalized Domain Names for Applications (IDNA 2008)
Defines how international domain names are encoded for use in DNS and email addresses.
RFC 3696: Application Techniques for Checking and Transformation of Names
Practical guide for validating email addresses, URLs, and domain names in applications.
RFC 5246: TLS Protocol Version 1.2
Defined TLS 1.2. Obsoleted by RFC 8446 (TLS 1.3). Still widely deployed but being phased out.
RFC 8446: TLS Protocol Version 1.3
The current TLS standard. Mandatory reading for secure SMTP (STARTTLS/SMTPS) and IMAP/POP3 over TLS.
RFC 9051: Internet Message Access Protocol (IMAP) Version 4rev2
The current IMAP standard for online mailbox access, folder management, and message retrieval.
RFC 2595: Using TLS with IMAP, POP3 and ACAP
Early TLS-for-email RFC. Obsoleted by RFC 8314 which mandates implicit TLS over the legacy STARTTLS approach.
RFC 8314: Cleartext Considered Obsolete: Use of TLS for Email Submission and Access
Mandates TLS for SMTP submission (port 465/587), IMAP, and POP3. Declares cleartext email protocols obsolete.
RFC 2049: MIME Part Five: Conformance Criteria and Examples
Defines MIME conformance levels and provides worked examples for implementers.
