Sendmail and spam filtering...
 

Hi,

I have set up an access list for sendmail and it seems to be working. However, I would like to make it more robust. I would like to block external subnets if that is possible. Something like xxx.xxx.xxx.xxx/23? Is this possible or do I need to continue to block IP Ranges instead.

Thanks,
-Me

If you overall subnet is something like 192.168.1.0/16 and you want to excluse something in between, you'll need to exclude the IP ranges. It's different is those external subnet were on completely different networks.

I might be wrong but I've never come any option in any mail server (sendmail, postfix, qmail) that enables you to omit certain subnet from a network.