API for sending/recieving E-mail WITHOUT using pre-installed email clients' settings!

I'm trying to make an E-Mail client for a customer (just something with different functionality than outlook). I've read some documentation on MAPI, but it seems too integrated with Outlook (or whatever the default email client is). I want to make my program completely standalone, separate from previously-installed email clients. I already know how to access the email servers via the Winsock control and send/recieve email from them, but I dont know how to handle HTML, attachments, embedded pictures, etc...! Is there any API that would let me do this without using pre-installed email clients or objects?

Thanx in advance!

Oh, and do I need to mention that I'm using Visual Basic 6.0 for this?