1. A system for providing a messaging application program interface (API) for use in a computing environment such as a data center, middleware machine system or similar environment, comprising: a computing appliance which includes one or more processor nodes for executing one or more application environments; a communication fabric connecting the one or more processor nodes and the application environments executing thereon; and a message bus implementation and messaging API that enables messaging within the computing appliance utilizing the communication fabric, including enabling a first application environment at a sender to issue a request to communicate message data to a second application environment at a receiver, allocating space in the sender's memory for storage of the message data, communicating a notification to the receiver providing the location of the message data, requesting by the receiver that the message data be retrieved from the location at the sender, and transferring the message data from the sender to the receiver asynchronously with providing the message data to the second application environment and providing a receipt to the first application environment.