Hi, when you do a major update to Windows, it often asks about what to do with your existing data. One of the options is to preserve it in a temporary folder named C:\Windows.old that Windows keeps for about 28 days. '''Can you find such a folder on your system?''' ''If so:'' Before proceeding, please set Windows to show you hidden files and folders: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files Then check here: C:\Windows.old\Users\''your-user-name''\AppData\Roaming\Thunderbird\Profiles '''Can you find that folder?''' If you have a profile folder there, and it has recently updated contents, then you should be on track toward finding your old mail folders and address book.