Openfire ships a proxy to be used for file transfer. When unconfigured, this proxy binds to the first available InetAddress on the server, and broadcasts the first available IP address. This can lead to problems, depending on the network setup. When a server resides in both a private as well as a public network, there's a good chance that the one address that's advertised is one that's unavailable to the intended users.
Instead of one address, the file transfer proxy should lists all interfaces on which it is reachable (unless configured otherwise).