Port forwarding is a feature available in most routers that allows you to forward external requests to the correct device/application on the local network.
In this case the purpose is to allow remote access to InboxGuardian even though it is installed and running on a local network.
Lets say, for example, you are on the road and want to check InboxGuardian for your clean, spam free email. The email account on your mobile phone is set to your routers external IP address. The router picks up the signal from your mobile phone but doesn't know what to do with it next. With port forwarding set up correctly you can instruct your router to forward specific requests to an IP address and port number on the local network, therefore allowing you to access your clean, spam free email from remote locations.
To add to the example above lets say your copy of InboxGuardian is running on 192.168.0.100 and port number 90 within your local network. Your external router IP address is, for example, 126.96.36.199. You set up port forwarding on your router so that any connection to 188.8.131.52 on port 100 forwards to local IP address 192.168.0.100 at port 90.
So when your mobile phone connects to your router using the IP address 184.108.40.206 and port 100 the router knows to forward that request to InboxGuardian, which is running on 192.168.0.100 at port 90.
Every router is different so please check with your router manufacturer for details on how to set up port forwarding.
For a further explanation of what port forwarding is click here.
If you are having difficulty please contact support.