Rated 5 out of 5 stars
Get it from http://mailredirect.mozdev.org/installation.html - mailredirect.xpi works with Thunderbird 7 but don't open it; instead:
Download it to your disk (right click on mouse to save on hdd).
Then open Thunderbird and its Add-On-Manager. Then click on downloaded xpi.- file on your disk just once and put/moove it via drag & drop to the Add-On-Manager TB. That was the only way it worked for me using TB 7.xx !