They do not sound like thunderbird files. Thunderbird can open individual email files which you might have saved as a separate file and they have a '''.eml '''extension and text files with same name as folder eg: Inbox - that do not have any extension (mbox files) and can be imported back into Thunderbird. re :$AppData$\Local\Profiles\ Your profiles are not stored in the $AppData$\'''Local''' folder. The only place I can think of that has files as you describe: Eg:- (0b5a9684e…………). (0ffd267235…………) And they are cache files which are located in: C:\\Users\User nameAppData\Local\Thunderbird\Profiles\profile name folder\cache2\entries folder and you can clear the cache via Preferences > General - under 'Network & Disk Space' They are not emails. The profile is stored in the 'Roaming' folder. * C:\\Users\User nameAppData\Roaming\Thunderbird\Profiles\profile name folder If you ever performed a backup then you would have copied the Roaming\'Thunderbird' folder to an external drive. If you had to recover OS then Windows would have created a 'windows.old' folder and put it on C: drive. That 'windows.old' folder would be available for about 30 days before Windows deletes it and it should contain: C:\\Users\User nameAppData\Roaming\'''Thunderbird'''\Profiles\profile name folder The 'windows.old' folder is used to recover the Thunderbird profile. If you have a 'windows.old' folder then you need to get a copy of the 'Thunderbird' folder and put it somewhere useful like desktop or external drive as it is your backup.