This article looks nice:
Charon Internet - ASP.NET: "Create an SMTP mailserver for ASP.NET"

There's no reason you can't do whatever you'd like with .NET, almost in spite of the fact that there are so many Wizards, shared libs, etc, that try to do even the simplest thing for you. The above article shows how to talk SMTP to an SMTP server, which is perhaps one of the simplest useful things you can do with TCP/IP. Heck, most SMTP servers, as was pointed out to me a while back, will walk you through sending mail with them: 

help

214-This server supports the following commands:

214 HELO EHLO STARTTLS RCPT DATA RSET MAIL QUIT HELP AUTH TURN ETRN BDAT VRFY

rcpt

503 5.5.2 Need Mail From: first


Anyhow, it's nice to see someone rolling their own SMTP connection with what's often an overly automated tech (rather, a tech where people use overly automated solutions).