Single SMTP server behind Firewall

In this configuration our SPAM Filtering software is installed on the same server as your SMTP software. The server only has one IP address available, SPAMFilter should be configured to listen on a port other than 25 so it does not conflict with your SMTP Server, for example port 26. Your SMTP software will not need be reconfigured.Reconfigure the firewall to perform port mapping so that it routes the external SMTP traffic from port 25 to port 26 on the IP assigned to SPAM Filter.If the firewall does not support port translation, this configuration can't be implemented. Please refer to the "Single SMTP server with a single IP address directly connected to Internet" example above for an alternate solution.