A subscriber typically receives messages while it is active. Some applications might require that a subscriber receives all messages even if the subscriber is inactive when the messages are published. In order to meet this requirement, you can create a durable subscriber. A durable subscription guarantees message delivery. A durable subscription is registered with the SonicMQ Broker with a unique identity; the broker retains the subscription's messages until they are received by the application or until they expire. The application can pass a JMS properties selector expression to the subscribeprocedure to specify which messages the subscriber wants to receive. The application can also specify whether it wants to receive its own published messages. Use the cancelDurableSubscription procedure to cancel a durable subscription.