I am evaluating jabber servers to find a suitable solution for a chat server that will scale well and work with Apple Push Notification Service for iPhone clients. I see that Openfire has a plugin architecture. Can anyone comment on the viability of a plugin that would notify off-line users of pending chat messages through the APNs service. Without diving into the technical details of APNs, is it relatively easy to intercept the messages and determine that a user is off-line in a plugin? Has anyone done any work with Openfire and APNs?
Also, I would like to get some feedback on how well Openfire will scale for a non-enterprise service with tens of thousands of simultaneous users.
Bonus points for anyone that can comment on implementations using Openfire with Google App Engine.
Thanks in advance!