Disable Basic Authentication
If you want to use a method that is more secure and doesn't prompt the user for a name and password, or if you don't want to grant users permission to log on locally on Internet Information Services (IIS), disable basic authentication. Remember that users cannot log on to the computer running Exchange until one of the authentication methods that the client supports is enabled on the server. If you disable basic authentication, make sure you choose another authentication method.
To disable basic authentication: