Message Journaling is a FioranoMQ 2009 feature that allows an application to replicate the messages arriving at a destination to a destination of a similar 'type'. For example, if messages are sent to a Queue named 'PRIMARYQUEUE' and 'MessageJournaling' is enabled on this queue, then all the incoming messages are replicated and then sent to a journaling destination, say 'JOURNAL_PRIMARYQUEUE', which is also a Queue.
Message Journaling essentially means to copy a message from one destination to another destination of similar 'types'. So, when Journaling is enabled, a console-based application can be written in order to consume messages from the original destination as well as from the journaling destination. This application can programmatically receive the originally produced message and inspect this message in any manner required.