It gets even more confusing :) For an MDB, using JMSContainerInvoker (I'm not sure if JCA 1.5 inflow shows the same behaviour) and with ack mode AUTO_ACKNOWLEDGE, the message is received by the connection consumer before handing off to to the MDB, therefore for an MDB and AUTO_ACKNOWLEDGE the message is acked *before* the MDB onMessage is executed, which is the opposite of what happens for a standard non MDB MessageListener. Nice. The more I delve into the MDB container, JCA 1.5 inflow, and JMS message delivery, the more I realise how full of contradictions, badly specced/unspecced areas and inconsistent behaviour this area is. :) View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4001298#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...