You should post in the App Gallery forum, they would probably be able to provide that information.
If your printer is on a relatively current firmware, you could just use the service with the Network Troubleshooting enabled and just take a gander via Wireshark to see where it goes
Well we are trying to use @printbyxerox. It never loads on the panel. I have narrowed it down to the xerox IP filtering which we only allow IPs in our company's range, and what I know of for xerox IP's. When I turn off IP filtering, @printbyxerox loads up fine. We need to use IP filtering because of our lack of good firewall options. Does anyone know what IP addresses I need to whitelist for @printbyxerox or any other services - but especially @printbyxerox ? I went through support, which directed me to another support request page, then received a phone call to post my question here.