Message grouping is more to do with consumers than producers, altho it is the producer that sets the message property.
If you use message groups then the order is preserved across multiple consumers on the same queue. It does this by pinning a single consumer to a specific group so that consumer will always receive those messages. If you only ever have a single consumer on a queue then order is guaranteed anyway.
NB. currently message grouping only works on a singler server, i.e. not across a cluster, so if you are using a cluster you will have to make sure that each set of grouped messages ae sent to the same node. This will be rectified for GA
I'm not using a cluster but what about across a bridge? Is order preserved if I use one.
But back to the my previous question, do I need to use the property "JMSXGroupSeq" or can I omit it when using groups?