All Email Security Gateways firmware version 3.5 and later.
Currently, the Email Security Gateway can have only one SMTP port open at a time. It is recommended that you use Network Address Translation (NAT) at your internet border firewall to route mail from a secondary port on the external IP address to port 25 on the Spam Firewall. Some firewalls, however, do not allow multiple ports on external IP addresses to be mapped to a single port on an internal IP address. The workaround in such cases is to allow the firewall to direct the chosen secondary port to the Spam Firewall unmodified and for the Spam Firewall to redirect the traffic to its own port 25 using Port Forwarding.
To configure Port Forwarding on the Spam Firewall, navigate the administrative web interface to the Advanced tab and then to the Advanced IP Configuration page. Once there, identify the Port Forwarding section. For each IP port to forward, enter the desired secondary SMTP port number as the Source Port, the internal IP address of the Spam Firewall as the Destination IP address, and port 25 as the destination port number. Click the Add button to store the new setting. Upon completion, the Spam Firewall will route traffic from the secondary SMTP port directly to its own port 25.
Be careful in your designation of a secondary SMTP port number so as not to choose a port that the Spam Firewall needs for other functions (see Solution #00004002 for the complete list of ports and protocols).
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