A user-defined output node is an extension to the broker that provides a new message flow output node in addition to those supplied with the product.
If you want your message flow to send messages using a protocol that is not supported by WebSphere Message Broker you can create your own output node to do this.
If the target application expects to receive message in any other way, you must use a user-defined output node.
User-defined output nodes can be considered together with user-defined message processing nodes. Conceptually, these two kinds of user-defined nodes are the same. Although a message processing node is typically used to process a message, and an output node is used to provide an output, in the form of a bit stream, from a message, you construct output nodes and message processing nodes in a similar way, and you can use either type of node to perform either function.
For more information on user-defined output nodes, read the topics that cover user-defined message processing nodes.