iptables -t nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 25 -j REDIRECT --to-ports 25

So anything outbound from eth1 (lan connection) on port 25 gets redirected to port 25 localhost which has its own smtp server running..


----------------------

add to /etc/sysctl.conf

net/ipv4/neigh/default/gc_thresh1=32768
net/ipv4/neigh/default/gc_thresh2=65536
net/ipv4/neigh/default/gc_thresh3=262144
net/ipv4/route/gc_elasticity=8
net/ipv4/route/gc_interval=30
net/ipv4/route/gc_min_interval=2