Undelivered Message Queue in EMS

If a message is to be removed from the system in any way besides being properly consumed by a message consumer, the server checks the message for the JMS_TIBCO_PRESERVE_UNDELIVERED property.
When JMS_TIBCO_PRESERVE_UNDELIVERED is set to true, the server moves the message to the undelivered message queue.

$sys.undelivered
This undelivered message queue is a system queue that is always present and can not be deleted.