You could use a script, but if all you want to do is pop up a new email message on your reader's computer, you can use the mailto: link and a couple of MT includes. I use a link like this on my website.
CODE
<a href="mailto:dummy@dummy.org?subject=<$MTEntryTitle$>%20-%20from%20willski.com&body=<$MTEntryPermalink$>">Email this topic</a>
I have it in my site near the bottom of each post. Just make sure the link goes inside the tag, or it won't work right. You can't have any spaces, or the link gets borked. Use %20 anytime you need to include a space.
Hope this helps!
///Will