The UPN (User Principal Name) suffix is the domain portion of the UPN (User Principal Name), such as @omnisecu.pvt for the UPN (User Principal Name) email@example.com. We can configure alternative UPN (User Principal Name) which provide additional security or simplify the naming if you have multiple-level child domains. For example, if you had the child domain florence.italy.europe.omnisecu.pvt, the default UPN (User Principal Name) suffix would be @florence.italy.europe.omnisecu.pvt. A user account ktom logging in to that domain would have a UPN (User Principal Name) of firstname.lastname@example.org. This is somewhat difficult and it is possible to create an alternative UPN (User Principal Name) suffix for logon purposes like email@example.com. This is much easier and secure for the user.
To create an alternative UPN suffix, open the Active Directory Domains and Trusts administrative console, right-click the root container and select Properties.
Inside the UPN (User Principal Name) dialog box, enter the name of the UPN suffix you want to add and then click Add. It is not necessary to type in the @ symbol here. Click Apply and OK to exit the dialog box. When you create a new Active Directory domain user next time, this new UPN (User Principal Name) suffix also will be listed in the Active Directory domain new user dialog box.