RFC 821 - Simple Mail Transfer Protocol (SMTP)
RFC 822 - Standard For The Format Of ARPA Internet Text Messages
RFC 974 - Mail Routing And The Domain System
RFC 1123 - Requirements for Internet Hosts -- Application and Support
RFC 1652 - SMTP Service Extension for 8bit-MIMEtransport
RFC 1842 - ASCII Printable Characters-Based Chinese Character Encoding
RFC 1869 - SMTP Service Extensions
RFC 1892 - The Multipart/Report Content Type for the Reporting of Mail System
RFC 1893 - Enhanced Mail System Status Codes
RFC 1894 - An Extensible Message Format for Delivery Status Notifications
RFC 1939 - Post Office Protocol - Version 3
RFC 1957 - Some Observations on Implementations of the Post Office Protocol (POP3)
RFC 2197 - SMTP Service Extension for Command Pipelining
RFC 2045~2049 - MIME
RFC 2554 - SMTP Service Extension for Authentication
RFC 2246 - TLS POP
RFC 2202 - Test Cases for HMAC-MD5 and HMAC-SHA-1
RFC 2831 - Using Digest Authentication as a SASL Mechanism
RFC 1321 - The MD5 Message-Digest Algorithm
RFC 2195 - IMAP/POP AUTHorize Extension for Simple Challenge/Response
RFC 2222 - Simple Authentication and Security Layer (SASL)
RFC 2554 - SMTP Service Extension for Authentication
The NTLM Authentication Protocol（非国际标准，msn pop）
http://davenport.sourceforge.net/ntlm.html#theType1Message