I think you'd have to "hack" it in this case, as ASP is not multi-threaded. MMMMMMM.... multi-thread.
Ahem. Excuse me. ;-)
I think you could fake it pretty well here by having another page do the emailing, and then just popping that page in a popup, and closing it when it's done.
To avoid the window popping up in your users' faces, you'll need to take the focus away from it, though.
function doEmail(){
var url = 'emailIt.asp';
var x = window.open(url,'emailWin');
window.focus();
}
so that the function fires off the popup, immediately takes focus back to itself, and then that window can do it's thing, and then close itself.
Granted, not an ideal solution, but one that I think could work quite well.
Store any vars you'd need to stick in that email in session variables prior to opening the window, and then just grab them back up on your email page.
Haven't had much chance to study up on .NET, but I know my fingers are crossed for multi-thread.
good luck!

paul