my local network is connected to internet with dial-up DSL.
linux Gateway: eth0: 192.168.0.1, ppp0
Windows mail server(exchange): 192.168.0.200 port: 25 + 110

I want to enable my LAN users to send/receive emails
to/from "outside" by using iptables.
I use following rules but it doesn't work.
What do I need to add to my rules...
such as mapping for the real IP (6.5.4.3) on ports 25, 110 pointing the exchange server


Can any body help me in this issue?

Thanks



#!/bin/sh

modprobe ip_tables
echo "modprobe iptables"
modprobe ip_conntrack
echo "modprobe ip_conntrack"
modprobe ip_conntrack_ftp
modprobe ip_nat_ftp
echo "modprobe ip_conntrack_ftp"
modprobe iptable_nat
echo "modprobe iptable_nat"
#modprobe ipt_MASQUERADE
#echo "modprobe ipt_MASQUERADE"

iptables -X;
iptables -F;
echo "iptables -f"
iptables -t nat -F;
echo "iptables nat F"
iptables -t mangle -F;
echo "iptables mangle F"
#iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
#iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1440
#iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1440
echo "SET MTU 1440"

iptables -t nat -A POSTROUTING -s 192.168.0.11 -o ppp0 -j SNAT --to 6.5.4.3
echo 1 > /proc/sys/net/ipv4/ip_forward