I hope this will help domain admins who want their users to sign-in to their workstations using different suffix instead of the default one.

Just to explain this better, let’s assume there is an internal domain name called “MYDOMAIN.COM“. So your users will be currently login in to their workstations using one of these two suffixes by default:

1. MYDOMAIN<username>
2. <username>@MYDOMAIN.COM

For example, if the username was Bill.Gates, the user will need to use either MYDOMAINBill.Gates or Bill.Gates@MYDOMAIN.COM to sign-in to a workstation in your domain.

If you want the user to use something different this is the way to do it:

1. Open up Active Directory Domains and Trusts
2. Right-click on Active Directory Domains and Trusts and choose Properties.
   
3. Type what you want to sign-in as under Alternative UPN Suffixes and click on Add.
4. Now go to the properties of the user account in AD that you want to change, and go to Account tab.
5. Under User logon name, you should be able to change the suffix to one of the suffixes you added. For example if you added a suffix like YOURDOMAIN.NET, now you can change the user to login as Bill.Gates@YOURDOMAIN.NET to a workstation in MYDOMAIN.COM domain.

Unfortunately you still cannot login as YOURDOMAINBill.Gates, as the workstation is not connected to such a domain.

I hope this helps.