Recover Deleted Messages is a handy Thunderbird add-on which will allow you to recover deleted messages, if the folder has not been compacted yet.
To use Recover Deleted Messages, select the folder, right-click and choose "Recover deleted messages", then follow the messages in status bar.
From the 0.2 version, Recover Deleted Messages should be able also to recover deleted messages from Imap folders, if they're set for offline use.
Recover Deleted Messages is localized in english and italian.
The Recover Deleted Messages add-on is cross-platform and it works on Mac OS X, Windows and Linux.
Requirements:
· Thunderbird 2.0 or later