SMTP on Port 26

To open up a new port (26) and redirect all packets to port 25, use

iptables -t nat -A PREROUTING -p tcp -d 192.168.0.1 --dport 26 -j DNAT --to 192.168.0.1:25

--dport 26 does the redirection job. pblinux pointed the following for Ensim Pro 4.0.1 on RHEL

/sbin/iptables -t nat -A PREROUTING -p tcp --dport 20025 -i eth0 -j DNAT --to xxx.xxx.xxx.xxx:25