How to redirect ports inside same machine using IPTABLES

As my mail server is running on port 8056, I got ended up searching to find a way to redirect all the mails which comes to port25 to port8056.

Below is one way of doing which helped me using iptables entry.


sudo iptables -t nat -A OUTPUT -p tcp -d 127.0.0.0/8 --dport 25 -j REDIRECT --to-port 8056
sudo iptables -t nat -A OUTPUT -p tcp -d x.x.x.x --dport 25 -j REDIRECT --to-port 8056
sudo iptables -t nat -A PREROUTING -p tcp --dport 25 -j REDIRECT --to-ports 8056


In the above commands

command 1 is to, forward port25 requests to port 8056 which are initiated via localhost. (i.e) telnet localhost 25.
command 2 is to, forward port25 requests to port 8056 which are initiated via IP address. (i.e) telnet x.x.x.x 25.
command 3 is to, forward the other network m/c requests to port 8056 through port25.