By default, When you install Exchange 2016 the default authentication method will be Domain\ User name. wherein some of the companies they feel uncomfortable to enter Domain\User Name. Let’s see how to change to User Name alone for authentication.
Login to Exchange Admin Center,Select Server–> OWA and Click on Edit
Under Authentication–> Select User name only and Browse to Select Domain
Select Windowstechpro.com and click on OK
Now you can see that it is asking for User name and Password only