Find all UPN suffixes used in a Active Directory (PSH)

Very short script for fetching all UPN-suffixes used in a Active Directory using ADWS:

Import-Module ActiveDirectory
$users = get-aduser -filter * -properties UserPrincipalName  | where {  $_.userprincipalname -ne $null }
$upnlist=@()
foreach ($i in $users)
{
$s = $i.UserPrincipalName.tostring()
$upn  = $S.substring($s.IndexOf("@"))
$upnlist+=$upn
}
$upnlist | Group-Object