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9.7. Message Failure, Component by Component

Once a message is accepted by a gateway it will not be lost unless sent within the ESB using an unreliable transport. JMS, FTP and SQL are JBossESB transports can be configured to either reliably deliver the message or ensure it is not removed from the system. Unfortunately, HTTP cannot be configured in this way.
The ServiceInvoker will place undeliverable messages in the re-delivery queue if they have been sent asynchronously. Synchronous message delivery that fails will be indicated to the sender immediately. In order for the ServiceInvoker to function correctly, the transport must indicate a failure to deliver to the sender unambiguously. A simultaneous failure of the sender and receiver may result in the message being lost.
JMS Broker
Messages that cannot be delivered to the JMS broker will be placed within the re-delivery queue. For enterprise deployments, a clustered JMS broker is recommended.
Action Pipelining
It is important to differentiate between a message being received by the container in which services reside and it being processed by the ultimate destination. It is possible for messages to be delivered successfully, only for an error or crash during processing within the Action pipeline to cause its loss. As mentioned, it is possible to configure some of the JBossESB transports so that they do not delete received messages when they are processed. This so they will not be lost in the event of an error or crash.