Try this: highlight inbox, rightclick, select properties and then select repair.

Merci de votre suggestion. malheureusement le problème n'est pas résolu. auriez vous une autre solution ? Merci

Is this an IMAP account? If so, my first suggestion would be to exit Thunderbird and, with windows file explorer, locate the profile and delete the inbox, inbox.msf entries for the account. If unfamilar with profile folder, - click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - exit thunderbird - you are now in profile. click the imapmail folder, then the 'account' folder and the inbox and inbox.msf should be visible. delete them. - on restarting thunderbird, the folder will be recreated. And I HOPE that resolves the issue. I am not experience well in troubleshooting mode, so the problem may need guidance from someone else if my suggestion does not work.