Make sure that oyur server has a real world name for its server name, and that name is set in your external DNS, then set port forwarding on your router from your external IP to your servers internal IP for the ports list in the attached image.
The other port you may need to open is for Server to Server Connections, which I believe is 5269. Doing this works well. I have my server configured in this way. It has a virtual 10.x.x.x address but a real world IP port forwards to the server. I just made sure that the server had a vailid external name when i configured it.
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I am not sure if you will need to re-add the users if you rerun the setup. I would doubt it though. To rerun the setup without a reinstall edit your openfire.xml file and change the setup tag to false: