The clients are calling send() on the same MessageProducer instance, and this isn't synchronized. This hasn't caused any noticeable problems in the past (when the MessageProducer was using ActiveMQ) or since we started evaluating JBM (although the loads on those 2 servers are still very low). This makes me think I really should queue up the messages to be sent myself and have one thread call send(), which will also get rid of the blocking problem. As for the exception listener stuff - yes, I understand how that works with the different re-connect values and it makes sense. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4242374#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...