HTML message formatting? It's going to be the same as any other HTML formatting. Rendition? You mean text versus HTML?

Its not the same as any HTML formatting. Different email programs render HTML emails differently based on the program. I've researched and found varying information about how best to create an HTML email (CSS yes/no? - embedded tables yes/no? - using divs yes/no?) and would be very interested in finding others who have experimented with this...as well as other email topics.

OK, thanks for the clarification. Here is a good discussion topic here at WebmasterWorld that should get you started ...

The Challenges of HTML Email [webmasterworld.com]

I've dabbled a little and it's a pain in the a**. You have outlook, thunderbird, webmail and a host of other clients to deal with. I even posted a similar message here 6 months or so ago but didn't get much feedback, so I'll try to help with the little I learned.

Outlook will destroy most good html and turn it to hogwash. So in my experience the limiting factor is Outlook, so you'll have to cater (unfortunately) to it, as Thunderbird is more standards aware. If you nail these two, you're on your way. I can't give stats on email client use around the world, though that would be helpful to have.

Some tips:
1)provide html and txt version of the email
2)make sure all image urls give the full location (http://...)
3)Since you're probably a small fry like me, it's not a bad idea to mimic what the larger companies are doing (who have the budget to research it). So if you get html spam/newsletters from Bank of America, or GoDaddy, or ebay or etc, then study their code.

Good luck

Thanks to both for your feedback.