$users = Get-ADUser -Filter * -SearchBase "O" -Properties proxyAddresses | select proxyAddresses

$gn = Get-ADUser -Identity $users | Select -ExpandProperty Givenname
$sn = Get-ADUser -Identity $users | Select -ExpandProperty Surname
$login = Get-ADUser -Identity $users | Select -ExpandProperty Samaccountname

$Users | ForEach-Object {

Set-ADuser -identity $users -remove -add {proxyaddresses="SMTP:*";proxyaddresses="SMTP:$gn.$sn@domain.com"}
Set-ADuser -identity $users -add {proxyaddresses="smtp:$login@domain.com"}

}