How the acknowledge process of a MDB occurs when we are working with CMT and we declare the onMessage() method as NotSupported. Does it occur? If so when? At the end of the onMessage()? At the beginning of onMessage()? Is it undefined? Also, is the tag value going to be considered in this case? I found a page which discuss on the transaction-type attribute, http://java.sun.com/blueprints/qanda/transaction_management/index.html