Message-driven beans were designed to operate within the context of JMS implementations with messages sent by a JMS Server. This does not mean Message-driven beans can not process messages sent by e-mail, HTTP, FTP, or any other protocol. As long as the server is able to convert these protocols into a JMS message (simple encapsulation will normally do), it can be handled by a Message-driven bean.
If the messages are defined in an open, extensible language like XML, unparalleled interoperability can be achieved in loosely-coupled systems using a model that is easy to understand. This means that Message-driven beans have the potential to become the de-facto model for handling any message type.