I stumbled across Dave Wanta's new FAQ Web site, http://www.SystemWebMail.com, which has the be the definitive place for information on the .NET Framework's System.Web.Mail namespace. Dave's got the info broken down into six sections, from quickstart examples and advanced examples, to tips on troubleshooting System.Web.Mail classes, to descriptions and links to the email-related RFCs. Quite a repository of knowledge, way to go Dave!
(Dave's expertise on System.Web.Mail comes from the several products he has created, such as aspNetEmail and aspNetPOP3. I have used both aspNetEmail and aspNetPOP3 before in my own projects, and have been impressed with the ease of using them, Dave's level of support, and their performance. In fact, you can read about how I am using aspNetPOP3 to help stop spam...)