I'm guessing it works with Outlook Express as that's what your pc is set up to use as a default mailing application?
You can try changing your default email client (temporarily) to see what happens. I'm not sure if you'll need to close and reopen the browser, or just click the submit button.
For the standards in html, you probably already know about w3.org.
http://www.w3.org/TR/html4/#minitoc
I'm not really a cave troll, but I do have an old PC running Linux near my desk at work. It's one of those with slot processors and ISA slots. Amazingly enough, my dad still has his first one from the 70s that uses 8-something-inch floppies. It still works, but it's not useful for much more than laughs. It's still good that you're considering a wider audience. *thumbs up*