Honestly, I would rather create a port
redirect, rather than change the port
which the mail server listens on. Then, you simply change the port
within your mail client. I have some IPTABLES examples on how to create Port
Add the Iptables rules to create the redirect so that any traffic going to port
26 is redirected to 25. In your mail client, configure SMTP to connect to your server on port
Let me know if you need any help.