An exception destination is used to handle messages that cannot be delivered to their intended bus destination.
Exception destinations prevent the loss of messages that cannot be delivered. If a message cannot be delivered to its intended bus destination, it can be rerouted to an exception destination.
Each messaging engine has a default exception destination, named _SYSTEM.Exception.Ddestinaton.me_name. This exception destination can be used to handle messages that cannot be delivered for all bus destination that are localized to the messaging engine. This enables administrators to access at one place all messages that cannot be delivered for a messaging engine.
Each bus destination can be configured with a non-default exception destination. This enables administrators to access at a unique place messages that cannot be delivered for the bus destination. An exception destination can be a local or a remote bus destination, but it must be a queue and it must exist when this destination is created. If the exception destination is not a queue or has been deleted when the message arrives, undeliverable messages are rerouted to the default exception destination for the messaging engine.
However, the service integration bus cannot guarantee the ordering of messages sent to an exception destination. Therefore, if message order is important, you can configure a bus destination to not use an exception destination. In this case, the Maximum failed deliveries limit specified for the destination is ignored, and the message remains available to consumers. Synchronous consumers repeatedly attempt to get the message; message-driven beans and other asynchronous consumers are repeatedly driven to consume the message. This can cause an increased load on the system. This situation continues until either the message is removed from the destination (for example, by an administrator using the WebSphere administrative console) or, for whatever reason, the consumer becomes able to process the message without rolling back.
Published messages are discarded if there are no subscribers.