Message Represents a single message and all its relevant settings.
 MessageProcessor Responsible for processing a single message.
 MessageReceiverCache A cache of receivers for a particular message type which MessageRouter implementations use for performance optimizations.
 MessageReceiverRegistry Registry for receivers of messages dispatched through a MessageRouter.
 MessageRouter The central message routing facility.
 MessageSettings Factory responsible for creating MessageRouter instances.
 ErrorPolicy Enumeration for the policy to apply for unhandled errors.
 MessageReceiverKind Enumeration for the different kinds of message receivers.
 MessageState Enumeration for the current state of a processed message.