I have two program versions: emclient-v10.0.3530 and emclient-v10.1.4588. Installing the first version was not possible, a message popped up saying “a later version of eM Client is already installed.
I also deleted all instance of “eM Client” in the registry and deleted all remaining e-M Client folder on the computer
If you are getting a message that a later version is already installed, then that means “your mail database was updated to a later version of eM Client” prior to you resetting Windows. So normally installing V10.1.4588 would have worked.
However as you have now deleted entries from the registry and also reinstalled the older V10.0.3530 over the top and it’s now wanting to repair or remove, “try the repair option”.
If the repair doesn’t work, then I would next close eM Client and then “rename the eM Client hidden database folder” to eg: eM Client-Old.
(Windows hidden eM Client database folder)
“Users\yourusername\AppData\Roaming\eM Client”
Then uninstall eM Client and “delete the database” if you get asked on the uninstall wizard.
Also if exists delete the following folder. C:\Program Files (x86)\eM Client
Then reinstall V10.1.4588 and setup as new.
If you still have eM Client install errors in Windows, then try the Microsoft installer / uninstaller troubleshooting tool. It still appears to work on Windows 11 even though is not stated.
Note: If you do run the Microsoft tool, “reboot your computer” before trying to install eM Client.
“How do I Fix problems that block programs from being installed or removed”.
https://support.microsoft.com/en-us/topic/fix-problems-that-block-programs-from-being-installed-or-removed-cca7d1b6-65a9-3d98-426b-e9f927e1eb4d
Now If eM Client still won’t install, then I would suggest to “create a new user Admin profile” and then reinstall V10.1.4588 and setup as new.
Lastly once you get it working, if you then had been making regular eM Client backups via the program either manually via the menu or automatically via eM Client Settings, you can then restore that from your eM Client dated backup.zip files from your “old user profile Documents / eM Client” folder via “Menu / File / Restore”.
Or you can restore a partial backup “from a previous eM Client backup.zip file”. or do a partial restore “from a previous hidden mail database folder”. See my post in the following thread on partial backup restores.
Also see the following eM Client support page on restoring a backup including restoring a partial backup “part way down the support page.