After installing Thunderbird, you would run Thunderbird for the first time and this would create a new default profile folder. Did you immediately create a new mail account at prompt and connect to server to download emails? OR Did you not create any mail account and instead exit Thunderbird. Then access the Profile folders and copy paste a backup of your old profile overwriting the new profile,... like this.... Access: C:\Users\<Windows user name>\AppData\Roaming\'''Thunderbird''' Delete the new default 'Thunderbird' folder. Paste the copied backup 'Thunderbird' folder into the 'Roaming' folder. Start Thunderbird. A Fresh Re-installation of my Windows 10 usually creates a 'windows.old' folder which should contain all your old profile info. Can you see a 'windows.old' folder on desktop ? OR Do you have a backup of the 'Roaming'/'Thunderbird' folder ? Thunderbird by default stores its profile here: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird This should be in the 'windows.old' folder. Do you have any backup of profile? Do you have any exported address books in LDIF or *.csv format ?