In Chapter 9, you saw the structure of a BizTalk message. You send BizTalk messages to your trading partners in a number of ways. Once you create a BizTalk message, you must wrap it in some kind of transport-specific envelope so that it can get somewhere.
Your BizTalk server should have a way of sending messages synchronously. In synchronous communication, the server sends a document to another BizTalk server and waits for a response. This is a basic requirement and is the least complex way to send messages.
In a production environment, however, you might be sending dozens or even hundreds or thousands of BizTalk messages from your application. If your application had to worry about getting a response from each request, you might end up with bottlenecks. Therefore, you should also have an asynchronous method of sending messages.