This article will show you how to add a new User Principal Name Suffixes or UPN to you Active Directory Forest.
UPN are being used as a login name If your Active Directory domain name is not the same as your actual public facing domain name, this is very useful If you are migrating to Office 365.
To add a new UPN, Open Active Directory Domains and Trust
Right Click on Active Directory Domain and Trusts and click on Properties
In Properties menu type the new UPN domain name, Click add and OK
Now when you will go to a user profile in AD you will see the new domain
