I have never coded HTML email myself, but a good friend of mine does. I have answered a few CSS and HTML questions for him; apparently HTML email has it's own set of quirks apart from normal HTML. My friend sent me a link to a site that is all about HTML email, so I thought I'd pass it on. If you are looking to learn about HTML email, this site would probably be very helpful.

Read more about HTML email at HTML Email Tips for Web Designers.