Hi,

i want to have Linux as front end firewall for my Email server.
so i assigned public ip address to Linux wan interface and did the following but its not working to get emails from outside domains.




iptables -A PREROUTING -t nat -p tcp --source x.x.y.y --dport 25 -j DNAT --to 192.168.10.50:25
iptables -A INPUT -p tcp -m state --state NEW --dport 25 -j ACCEPT

iptables -t nat -I POSTROUTING -s 192.168.10.50 -j SNAT --to-source x.x.y.y

iptables -t nat -A POSTROUTING -s 192.168.10.50 -j MASQUERADE



Right now there is no blocking rules on any table and Forwarding is also enabled on kernel

Your source in PREROUTING should not be your real IP, your source is any and your destination is your real IP.

You can also do this:
Replace eth0 for your actual Internet iface.