Originally Posted by potter

Oh, and per your actual question. There isn't any way to "force" the recipient to get the email in it's html format. That is their personal settings, and you can't just take control of their computer.

The best method, is to create two copies of the email on your server. One being a copy of the html email itself, and the second being a .txt copy - which just has the content/copy of the email and no html code. At the top of your email, add two links to these files like "View this email with images" and "view the text version of this email", that way if they aren't seeing it right, or have images turned off - you still have a good chance of getting them to see your ad / email.