Hi Winan,
Here another link you will find interesting.
http://www.byte.com/documents/s=126/byt19990816s0017/index8.htmIf you change your SMTP service to another port, it could cause unexpected result and many problems. However, if you chose to do so, consider port 25000 instead of 5000. I would assume that qmail run as a service (e.g daemon) under your RedHat Linux. Search through the qmail doc on configuration, or look through your qmail directories to find the configuration file and change the port setting to 25000. Then qmail will listen to port 25000 for incoming/outgoing mail. In this scenario you would probably need an agreement with your MX relay agent as any email sent over a non-standard port will hit again many firewall. If you are trying to establish a private network, you might look into a VPN. Also, any email being sent out from your locale network would need to be directed to port 25000, so you would need to change your email client like outlook express, outlook, mozilla, etc. to use port 250000 for all SMTP services.
