I just can't find any info on how to send HTML pages via a MAPISession, I'm not even sure if I can do this or not.

You can only send plain text using MAPI. If you must send HTML pages, look into Cdo for Windows 2000 or later. You can find documentation in MSDN under Platform SDK Documentation -> Messaging and Collaboration Services -> CDO For Windows 2000.

We also have an explanation of Cdo for Windows 2000 as well as a class and a sample form for using it in Chapter 4 of MegaFox: 1002 Things You Wanted to Know About Extending VFP