update rfcs

docs/reference/rfcs.md

@@ -4,10 +4,7 @@
 
 - [RFC 3463](https://datatracker.ietf.org/doc/html/rfc3463) Enhanced Mail System Status Codes
 - [RFC 5321](https://datatracker.ietf.org/doc/html/rfc5321) Simple Mail Transfer Protocol
-- [RFC 6376](https://datatracker.ietf.org/doc/html/rfc6376) DomainKeys Identified Mail (DKIM) Signatures
 - [RFC 6409](https://datatracker.ietf.org/doc/html/rfc6409) Message Submission for Mail
-- [RFC 7208](https://datatracker.ietf.org/doc/html/rfc7208) Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1
-- [RFC 7489](https://datatracker.ietf.org/doc/html/rfc7489) Domain-based Message Authentication, Reporting, and Conformance (DMARC)
 - [RFC 8314](https://datatracker.ietf.org/doc/html/rfc8314) Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access
 
 ## SMTP extensions
@@ -26,6 +23,12 @@ Available mechanisms list: https://www.iana.org/assignments/sasl-mechanisms/sasl
 
 - [RFC 4616](https://datatracker.ietf.org/doc/html/rfc4616) `PLAIN` The PLAIN Simple Authentication and Security Layer (SASL) Mechanism
 
+## SMTP security
+
+- [RFC 6376](https://datatracker.ietf.org/doc/html/rfc6376) DomainKeys Identified Mail (DKIM) Signatures
+- [RFC 7208](https://datatracker.ietf.org/doc/html/rfc7208) Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1
+- [RFC 7489](https://datatracker.ietf.org/doc/html/rfc7489) Domain-based Message Authentication, Reporting, and Conformance (DMARC)
+
 ## IMAP core
 
 - [RFC 3501](https://datatracker.ietf.org/doc/html/rfc3501) INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1