MSMQ supports two delivery methods: express and recoverable. Choosing between express and recoverable delivery is a matter of trading performance and resource use for reliability and failure recovery.
In general, express messages use fewer resources and have faster throughput than recoverable messages. However, express messages cannot be recovered if the computer storing the memory-mapped message files fails. Recoverable messages use more resources and have slower throughput than express messages, but can be recovered no matter which computer fails.
For example, if an MSMQ-based application is sending express messages to a queue through an MSMQ routing server, and the network link between the MSMQ routing server and the destination computer fails, the messages will continue to be stored in memory on the MSMQ routing server. If the MSMQ routing server is shut down before the network link is restored, the express messages are lost. However, if recoverable messages are used, the messages are not lost and are delivered after the MSMQ routing server and network link are brought back online.
The sending application, not MSMQ, specifies the delivery method.