-----Original Message-----
Better would be a rule to forward their connection to a honeypot / tarpit
box that would do what
you want ... tie up their connection for a while.
You don't have to have it forward to a separate box for the tarpit to work. Tarpit rules can be placed into the firewall so that any packets from a particular host (or network) get tarpitted, while allowing everyone else's to come through to the listening daemon. You just have to give it a specific source and port. The following would tarpit port 25 (TCP) for the IP address 99.99.99.99, while allowing everyone else through to the listening SMTP daemon:
iptables -I INPUT -s 99.99.99.99 -p tcp --dport 25 -j TARPIT
So it's just a matter of adding rules per each host that causes a problem.
-- Take care, Randall