Those IPs you have provided are internal ones. You can’t just connect to other internal network from another one if their are not connected and there is no router providing a connection between them. This other office must have an external Internet IP, also on this office’s router must be a forwarding rule, so when you try to connect to xxx.xxx.xxx.xxx (external IP of that office) to a port 5222, then router will forward your connection to an internal IP, say 192.168.2.100, which will be an IP of their Openfire server. Also, you can’t be connected to 2 servers at once and you must have an account on that second server. There is another option, to have a server-to-server connection between those two servers, but that could be even more difficult (also some other ports should be forwarded on both sides). In that case you would be able to chat with other server’s users while being logged in at your server.