If you work with computers long enough you'll eventually come to the realization that as soon as you come up with an idiot proof solution to something ... along will come bigger idiots. ;)
Outlook is one of the most popular mail clients out there. However, Microsoft threw a bit of a monkey wrench into the works with the latest version, Outlook 2007. They're using Word 2007's rendering engine now instead of IE, so that limits a lot of what will be rendered.