is a Thunderbird port of the Firefox FEBE
extension. Both work very similarly. While TEBE nor FEBE will automatically
sync your data, each can automatically upload backups to Box.net. These backups can easily be restored through the Restore (from online backup)
feature in the TEBE/FEBE menu.
The restores are destructive in the sense that they will overwrite existing data.
The FEBE FAQ
and Backup Tutorial
may answer more of your questions.