Sounds like you do not perform regular backups.

Do you see a 'windows.old' folder on the desktop?

If yes, look in that 'windows.old' folder. Typically it would have been in this location: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<Profile name>\

Does it have that 'Thunderbird' folder in it?

You may need to make hidden files and folders visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

If yes.

• Copy that 'backup 'Thunderbird ' folder.

• Exit Thunderbird if it is running.
• Locate the 'Roaming' folder on computer: C:\Users\<Windows user name>\AppData\Roaming
• delete the 'Thunderbird' folder that is in the 'Roaming' folder.
• Then, in the 'Roaming' folder, right click and paste the copied backup of 'Thunderbird' folder.

Start Thunderbird.

Hi Toad-Hall, I don't have a 'windows.old'-folder.

When you perform a complete reinstallation of Operating System, everything is wiped as if starting anew.

If it was an upgrade to Windows 10 or restore then usually there is a 'windows.old' folder created automatically by Windows.

re :When I use recover-software What recover software are you talking about?

There is an Thunderbird addon designed to recover deleted emails from non-compacted folders, but that is not the same as recovering deleted files after an OS reinstallation.

I tried software as Recuva, Hetman Partition Recovery, Stellar Phoenix Win Recovery,... As I did have a complete reinstallation I accept my mails are lost. Thanks anyway