How do I configure one or more protocols to be Internet-facing?

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Summary

Softalk Mail Server will require one or more ports to be Internet facing in the following conditions:

  • E-mail is received directly via SMTP. The MX Records of the domain need to point to an e-mail server that is Softalk Mail Server.
  • POP3 accounts hosted by Softalk Mail Server need to be accessed over the Internet
  • IMAP accounts hosted by Softalk Mail Server need to be accessed over the Internet

Detail

In a usual business situation the computer running Softalk Mail Server will not be Internet facing, but instead will be behind a router or firewall. The actual router will be the only device that has the external IP address(es); the other devices will have a non-routable IP address (usually 192.168.x.y or 10.x.y.z), these addresses are called non-routable as all routers will not route these addresses.

It is not possible to access these hosts from the WAN side of the router; therefore a technology called NAT (Network Address Translation) will need to be employed. Please see http://en.wikipedia.org/wiki/Network_address_translation for more information.
It is not possible to describe how to configure every router, it is recommend that you search for NAT or Network address translation in your router manual.

The Mail Server should first be configured with a fixed IP address; it is not good practice for a server to have a dynamic IP address.

For this example, let the mail server have an internal IP address of 192.168.0.22 and the router have IP address on the LAN side of 192.168.0.1

By visiting the IP address of the router on the LAN side using a web browser it is usually possible to configure various settings of your router. You may require a password to log into the router.

The router should have an option called Port Forwarding or NAT, go into this option.

To configure a rule for SMTP a port forwarding rule must be added.
Set the external port to 25, and set the internal address to 192.168.0.22 and the port to 25, you may need to enter 192.168.0.22:25 on some systems. This will route packets coming from the WAN side on port 25 to the host 192.168.0.22 on the LAN side to port 25.

Therefore if a client uses your external address then packets will be routed to 192.168.0.22 giving the impression that the mail server is listening on the external address on port 25. You can of course have different servers on your internal network on different ports, but this is completely transparent.

This can be achieved in exactly the same manner for POP3 and IMAP by entering the ports 110 and 143 respectively.

To find out your external IP address go to: http://whatismyipaddress.com/
It is common for the external IP address to be dynamic, changing periodically. In this case it is recommended that you set up an account with DynDNS http://www.dyndns.com/services/dns/dyndns/. DynDNS, DDNS allows you to create a hostname that points to a dynamic IP address.

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