"All these years of internet use later, HTML mail still sucks. You may think I mean 'HTML mail doesn\'t work properly in some e-mail clients.' And that statement is certainly true. Companies spend hours crafting layouts that may not work in Eudora or Gmail, or may no longer work in Outlook.
Even in programs that support the crap code used to create these layouts, all that hard visual work will go unseen if the user has unchecked 'View HTML Mail' in their preferences.
As for CSS, it is partially supported in some e-mail applications and in web apps like Gmail, but only if you author in nonsemantic table layouts and bandwidth-wasting inline CSS. Which is like using a broken refrigerator to store food at room temperature."