Sometimes the only answer is negative, and to be honest I don't know of any other way you can deal with it. The only way of checking if a browser would be capable would be to have two email messages.
And a LONG list, if its going to be sent to someone which you know has that capability, (most ISPs) then use the HTML one, if not, send the text one. Theres a lot of ISPs and free web mail out there, I was looking for once for a friend, I spent five minutes and sent him a list of 9 from my own knowledge and a single google search...
If you want to do it this way, hotmail doesn't support HTML 🙂