For those of you who have Plex servers and would like to stream your movies outside of your home network, and you have tried the following:
Setting your home router to forward the data coming out of the IP address of your machine containing the Plex server out through port 32400
Making sure your Internet provider did not include a router within their their gateway unit (with its own NAT settings), thereby screwing up your own router's attempt to assign the right IP addresses of your machines in your network to the outside world (AKA double NAT settings)
Then another option that you could try is, to call your Internet service provider (ISP) and ask them to provide you with a static IP address. Most ISPs will oblige if you ask. However, some may charge an extra fee for this.
In my case, I called my ISP and told them my problem with the Plex server not being visible outside my network, they seemed to immediately understand what I needed and told me that they would assign me a permanent outside IP and all I had to do was to check the next day. That did it. Now my Plex is visible outside my network.