Correct, there isn't a means to block DHCP leases based on MAC-addresses currently. Keep in mind that this functionality is relatively recent in DHCP servers. For windows DHCP, this wasn't possible until Server 2008 and then only with an unofficial addon and only became built-in with Server 2008 R2. If you'd like to see DHCP MAC-Address filtering in Astaro, you can enter a feature request at feature.astaro.com.
__________________ ACE v8/SCA v9.3
...still have a v5 install disk in a box somewhere.