For the Front Door Rejector,the IP Filtering seems only work with single IP,not support IP range.

It will be better if it support IP range,even though you can use IPTABLES to block IP range,but using the build-in function,you can see log at IPAttacker.log or FrontDoor.log and know which IP is blocked.

If you get attacked email with attachment 1-2 second per mail rate and each email is within 3MB,it will take up much CPU for clamav. 

With IP range support,IPAttacker can block it before content filter.

Hopefully it can be improved.