External CSS file is a no-no, because it might not get downloaded. Also keep in mind that Outlook has problems with CSS. Well, not Outlook itself, but Word which is the default email editor* (a problem in case a recipient wants to forward the email or reply to it). In Outlook 2007 Word is used also as renderer so much of CSS simply doesn't work.
I recommend avoiding HTML altogether if possible, but if you can't avoid it, keep it simple and oldfashioned, because anything else could easily be a problem (not displayed properly or filtered out).
* I made a mistake a couple of times of forgetting to turn on Word as editor when testing. Things suddenly broke apart when another user tried it with their default configuration. |
