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