Message Priority
The JMS specification includes a JMSPriority message header field in which senders can set the priority of a message, as a value in the range [0,9]. EMS does support message priority (though it is optional, and other vendors might not implement it).
When the EMS server has several messages ready to deliver to a consumer client, and must select among them, then it delivers messages with higher priority before those with lower priority.
However, priority ordering applies only when the server has a backlog of deliverable messages for a consumer. In contrast, when the server has only one message at a time to deliver to a consumer, then the priority ordering feature will not be apparent.
You can set default message priority for the Message Producer, as described in Configure a Message Producer. The default priority can be overridden by the client when sending a message, as described in Send Messages.
Also refer to JMS Specification, chapter 3.4.10.