I may be mistaken - but I think I remember someone once mentioning that acks can be sent asynchronously from the client to the server. I'm trying to understand how this can work, since it seems to me it can result in race concditions, for instance: Imagine the following: 1. Client acks message A asynchronously 2. Client calls session.recover() 3. (asynch ack hasn't arrived at server yet) - Server resends message A since it thinks it's not acked yet 4. Client receives message A again event thought they acked it. ?? Any ideas? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3956940#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...