I have seen this case many times before sometimes when creating a naming convention the domain name becomes very long ( it seems the older the organization the longer the name and a lot of domains with a lot of Childs ) . any way you will end up with creepy looking name like NT.ET.local.dom – imagine you have10 of those and one service desk – which is not something user friendly at all . to add friendly name you don’t have to recreate or migrate your domain as might thing all you have to do is to add a suffix .
You can use Active Directory Domains and Trusts to add user principal name (UPN) suffixes for the existing user account. The default UPN suffix for a user account is the Domain Name System (DNS) domain name of the domain that contains the user account. You can add alternative UPN suffixes to simplify administration and user logon processes by providing a single UPN suffix for all users. The UPN suffix is used only within the Active Directory forest, and it is not required to be a valid DNS domain name.
Open active directory domains and trusts
Go to properties
add the new suffix you want
now when you create user the new suffix would appear
to login you have to use the format username@domain , or it will give you an error ,
that’s all for now ,stay tuned