In order to Bulk change all users’s UPN Address in a single OU do the following:
Import-Module ActiveDirectory $oldSuffix = "oldDomain.com" $newSuffix = "newDomain.com" $ou = "OU=Users,OU=office,DC=dcname,DC=local" Get-ADUser -SearchBase $ou -filter * | ForEach-Object { $newUpn = $_.UserPrincipalName.Replace($oldSuffix,$newSuffix) $_ | Set-ADUser -UserPrincipalName $newUpn }