Cost of sending XMPP messages via Google App engine

Hopefully this question is allowed over here. It does not really have to do with programming 开发者_如何学Pythonper se but with the costs associated with it.

My question is:

"How much does sending/receiving XMPP messages cost".

I can find all the information about email etc. But I could not find information about costs sending/receiving XMPP messages.

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http://code.google.com/appengine/docs/quotas.html#XMPP

I think it has a fixed quota - not billable.

Not sure whether that means that you just can't go over your quota. You'd probably be best asking on the GAE-Java group http://groups.google.com/group/google-appengine-java