Mass/Bulk Changing User UPNs to the same as the user Email address

the only thing you should change is the $ou variable to represent the Searchbase.

In this example the searchbase goes 1 OU deep but you can change that ofcourse by setting another LDAP.

$ou = "<OU=Name of OU>,DC=<domainname>,DC=<extention>"

$users = (get-aduser -searchbase $ou -filter * | select -ExpandProperty Samaccountname)

foreach ($user in $users)

{

                Set-ADUser $user -UserPrincipalName (Get-ADUser $user -Properties mail | Select-Object -ExpandProperty mail)

}