Rated 5 out of 5 stars

TB3.1:
There is a version available on http://mailredirect.mozdev.org

Search for the link named
"Mail Redirect Extension 0.7.4 for Thunderbird 3.x".
Do not try to download v0.7.5 - this is the old TB2.x version!

This review is for a previous version of the add-on (0.7.5).