Today I spent some time compiling a list of all of the RFCs that our email hosting system supports.  See any I might have missed?…

1939	- POP3
2449	- POP3 Extension Mechanism

3501	- IMAP4rev1
2683	- IMAP4 Implementation Recommendations
2180	- IMAP4 Multi-Accessed Mailbox Practice
2088	- IMAP4 non-synchronizing literals (LITERAL+)
2177	- IMAP4 IDLE command
2342	- IMAP4 Namespace
2087	- IMAP4 QUOTA Extension
3348	- IMAP4 Child Mailbox Extension
3502	- IMAP4 MULTIAPPEND Extension
3691	- IMAP4 UNSELECT command
2221	- IMAP4 Login Referrals
draft	- IMAP4 Extension for SASL Initial Client Response

2821	- SMTP (updated rfc821)
3463	- SMTP Enhanced Mail System Status Codes
3464	- SMTP Delivery Status Notifications
2554	- SMTP Extension for Authentication
2920	- SMTP Extension for Command Pipelining
3207	- SMTP Extension for TLS
1870	- SMTP Extension for Message Size Declaration
1652	- SMTP Extension for 8bit-MIMEtransport
2476	- SMTP Message Submission (port 587)

1945	- Hypertext Transfer Protocol -- HTTP/1.0
2616	- Hypertext Transfer Protocol -- HTTP/1.1

2822	- Internet Message Format (updated rfc822)
2045..2049 - Multipurpose Internet Mail Extensions (MIME)
2183	- Content-Disposition MIME header
1894	- Message Format for Delivery Status Notifications
2298	- Message Format for Message Disposition Notifications
3503	- Message Disposition Notification profile for IMAP
3462	- Multipart/Report Content Type
3834	- Automatic Responses to Electronic Mail
2246	- The TLS Protocol Version 1.0
2595	- Using TLS with IMAP and POP3
2142	- Required abuse@ Mailbox Name
4408	- Sender Policy Framework (SPF) Version 1