Very interesting. I was about to tell you to check what is set up as the default app. In search type: default and select 'Default apps' So I checked this and discovered that my 'Email' did not have an app selected, which is weird. When I click on the 'option to select an app', thunderbird was not in the list. Thunderbird is not actually removed from computer. That would only occur if you uninstalled it or whether you performed a recovery so reinstalling the OS, in which case you would have a 'windows.old' folder on C: drive containing all your Thunderbird profile which can be used as a backup, but that 'windows.old' folder is only availabe for about 30 days. Baring in mind, I made a similar discovery that 'Thunderbird' was not set up as default and was not available in the default list, it is possible Thunderbird and Profile are all perfectly ok, you just need to tell the computer to use it. So start Thunderbird either using any of the shortcut icons or directly from either one of these locations as it just depends where it is installed. You click on 'thunderbird.exe'. * C://Program Files/Mozilla Thunderbird/thunderbird.exe * C://Program Files(x86)/Mozilla Thunderbird/thunderbird.exe then do this in Thunderbird. Menu app icon > Preferences > General Under 'system integration' make sure this checkbox is selected: 'Always check to see if Thunderbird is the default mail client on startup' Click on 'Check now' Select these checkboxes: 'Email', 'Newsgroups', 'Feeds', 'Always perform this check when starting Thunderbird' Click on 'Set as Default' If prompted, Allow computer to make changes. Then you will discover the computer 'Default apps' will have 'Email' showing as 'Thunderbird'. I checked to see if there were any updates in the Windows update history and did not find anything for a very recent date. But I do have a couple of updates that are available to install now. I've got a DELL computer which performed an update on the 9th of January and says it needs a restart, obviously closing computer and restarting next day did not install those updates.