Due to the way that Microsoft's synchronization API works, there's currently a limitation on which types of Microsoft accounts are supported by our sync engine.
In short, organizational accounts are supported whereas personal (free) accounts are not.
Supported:
Office365
Azure AD,
Other types of organization accounts
NOT supported:
Live.com
Outlook.com
Hotmail
Other types of personal accounts
Technical explanation
Microsoft is working on bringing Change Notifications (real-time sync updates) to personal accounts, but it's currently only released in their beta version of their API which is not ready for live usage.
You can see difference here:
Error message
If you try to connect with a personal account, you'll might see this error message from the Microsoft login screen:
AADSTS50020: We are unable to issue tokens from this api version for a Microsoft account. Please contact the application vendor as they need to use version 2.0 of the protocol to support this.