I am using Windows 7 and a POP email server in order to keep all the emails locally within my own system. In other words there should be a recovery method that is Thunderbird specific but also regarding my hard drive. The odd thing is I only delete emails from the folder itself and such deletions are slow as the computer ticks through and deletes one email after another. I don't know how these emails lost were deleted as there never was any time delay and possibly could have been done through the search function quite accidentally.