For quite a while I've blocked spam sources by IP address, especially coming from locations outside the country.  The method I've used is to find out what the assigned block is of the source and filter that in the header.  You have to use a [ in front of the IP address or SM will ignore it.  Another issue is we can't use a netmask or the /xx construct.

Would love to see a direct implementation of IP & netmask, or IP and subnet filtering capability.  This would give precise boundaries for a given IP block we want to filter out.

Much appreciated.

--Ben