On a Windows Server 2008 R2, I was trying to update Office from 2010 to 2016. I bought the Office 2010 Professional single install version (not 365) but left 2010 just in case we had to revert to it. I completely forgot Office 2016 doesn't allow a standard license on a server with Terminal Services on, so I proceeded to uninstall 2016. Upon reboot, users on the server and I are unable to set outlook 2010 as default anymore, so I followed the "Let me Fix It Myself" instructions in this article: https://support.microsoft.com/en-us/help/813745/either-there-is-no-default-mail-client-or-the-current-mail-client-can
However, when deleting all the Microsoft Outlook subkeys (the article wasn't clear on which ones as it simply said "delete the subkey", and the key in question had multiple) and repairing the Office 2010 installation from Control Panel, I'm unable to set Outlook 2010 as default, all Outlook icons are gone from "Set Default Programs" in the control panel. I may have deleted too many subkeys from the registry key (path: HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Microsoft Outlook), and i didn't back up the registry of course, smugly thinking it was a simple issue.
Is there a way to fix this? Maybe one of you has the same set up and can tell me the exact subkey structure (I'll of course update any file paths that may differ)?