You should not be using Mozbackup because it is very old and out of date and not maintained since 2012. On the website for Mozbackup the author clearly states '' "MozBackup is not being developed anymore. There are known issues and there is no time on my side to fix all issues and develop new features. Use MozBackup only on your risk. Thanks for understanding. " '' UPDATED re :the messages put in folders classified below incoming mail did not reappear . Worth seeing if a repair folder works first. * Right click on folder and select 'Properties * click on 'REpair folder' * click on OK re : ''After re install of W10 '' Did the reinstallation auto create a 'windows.old' folder on C: drive ? If yes, it may have auto backed up your profiles. Look for a 'windows.old' folder and see if it has this backed up in it: * C: Users/User name/Appdata/Roaming/'''Thunderbird''' If yes, then copy that 'Thunderbird' folder. Exit Thunderbrd if it is running. Locate the current default location in :C: Users/User name/Appdata/'''Roaming''' folder The 'Roaming' folder will contain a default 'Thunderbird' folder which you are currently using - delete it and then paste the copied 'Thunderbird' folder from backup into the 'Roaming' folder. then start Thunderbird.