Defined TLS 1.2. Obsoleted by RFC 8446 (TLS 1.3). Still widely deployed but being phased out.

The current TLS standard. Mandatory reading for secure SMTP (STARTTLS/SMTPS) and IMAP/POP3 over TLS.

The current IMAP standard for online mailbox access, folder management, and message retrieval.

Early TLS-for-email RFC. Obsoleted by RFC 8314 which mandates implicit TLS over the legacy STARTTLS approach.

Mandates TLS for SMTP submission (port 465/587), IMAP, and POP3. Declares cleartext email protocols obsolete.

Defines MIME conformance levels and provides worked examples for implementers.

Defines charset and language tagging for MIME parameter values, used in Content-Disposition filenames with non-ASCII characters.

Defines which IP addresses are authorised to send mail for a domain via DNS TXT records.

Original SPF specification. Obsoleted by RFC 7208 in 2014 with stricter language and clarifications.

Cryptographic signature standard that lets receiving MTAs verify a message was authorised by the sending domain.