A message is a discrete unit of information that one program wants to pass to another. The following examples are possible message types:

The message queuing computer does not impose any constraints on the content or format of messages exchanged via a queue, and neither does MSMQ Adapter.

When a program puts a message into a queue, the client envelops or wraps the message with control information such as routing information, priority codes, and message type. The term "message" also can refer to the entire message structure; that is, the control information in addition to the unit of information to be passed. In this context, the unit of information is usually referred to as the message body, the application data, or the user data. When this distinction is necessary, this book uses the term Body to refer to the content of the message.

To use queuing effectively, programs that communicate via a queue must agree on a common message content and structure. For example, if Program A is designed to pick up and process cXML-formatted purchase orders from a queue named "Orders", programs that interact with Program A must deliver properly-formatted cXML purchase orders to the Orders queue. Identifying the content and structure of the Body is a key activity that you must perform when designing a system that exchanges data through MSMQ Adapter.