I recently encountered a unique scenario when using Quest Migration Manager for Active Directory. I was in the process of migrating 3 AD Forests into a new AD Forest. I had already migrated 1200 users into the new AD Forest and at the time of migration the UPN’s were contoso.com.

My customer then decided to change all UPN’s and primary smtp domains to @fabrikam.com in the middle of the project. This caused a big problem when computer accounts were being migrated. After the computer account had completed migration to the new domain, the user’s UPN was @contoso.com. Which meant the user had to change their UPN to login instead of just simply entering their existing AD password that they were previously using.

So how do we resolve this issue.Right click on the properties of the domain pair as per image below
Next change target domain to contoso.com or a fqdn of a domain controller in contoso.com

Next modify the security settings and set the domain suffix to fabrikam.com
Finally stop and start the synchronization task.

Once this has been completed, when computer accounts are migrated the correct UPN will be populated and users simply need to enter their existing AD password.