Disable Microsoft Accounts in Windows 10
There is a Group Policy setting for disallowing user to log in using Microsoft accounts in Windows 10. It’s documented, however, that this setting does not work correctly (see this TechNet forum post). To get disable Microsoft accounts, you must add the following registry keys. You can still use a GPO to apply them, they just need to be under the registry key portion.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\PolicyManager\current\device\Settings]
“AllowYourAccount”=dword:00000000
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\PolicyManager\default\Settings\AllowYourAccount]
“value”=dword:00000000