The other aspect of reliability is ensuring that the broker does not lose persistent messages before they are delivered to consumers. This means that when a message reaches its physical destination, the broker must place it in a persistent data store. If the broker fails for any reason, it can recover the message later and deliver it to the appropriate consumers.
The broker must also persistently store durable subscriptions. Otherwise, in case of failure, it would not be able to deliver messages to durable subscribers who become active after a message has arrived in a topic destination.
Messaging applications that want to guarantee message delivery must specify messages as persistent and deliver them either to topic destinations with durable subscribers or to queue destinations.
Chapter 3, The Message Queue Broker describes the default message store supplied by the Message Queue service and how an administrator can set up and configure an alternate store.