Ok. I run my own email server (using Qmail - its awesome) but have recently discovered that I occasionally get spammed by some annoying locations, such as mrktmail.com. I figure - hey, lets block them at the iptables firewall level, so they can't connect via smtp.

I check the header of one of the spam mails and discover that they are on the subnet. So I block that subnet in iptables.

I do an iptables -l and among the rules is:

DROP all -- anywhere

So far so good.

But I'm STILL getting the spam mail.

What am I doing wrong here? ???