System.Messaging API is a low-level API that provides the basis for creating a messaging application. However, 'Out-of-the-box', System.Messaging leaves the act of creating sophisticated multi-threaded messaging servers and clients as an infrastructure activity for the developer. Spring fills this gap by proving easy to use helper classes that makes creating an enterprise messaging application easy. These helper classes take into account the nuances of the System.Messaging API, such as its lack of thread-safety in many cases, the handling of so-called 'poison messages' (messages that are endlessly redelivered due to an unrecoverable exception during message processing), and combining database transactions with message transactions. Other goals of Spring's MSMQ messaging support are to support messaging best practices, in particular encouraging a clean architectural layering that separates the messaging middleware specifics from the core business processing.
Spring's approach to distributed computing has always been to promote a plain old .NET object approach or a PONO programming model. In this approach plain .NET objects are those that are devoid of any reference to a particular middleware technology. Spring provides the 'adapter' classes that converts between the middleware world, in this case MSMQ, and the oo-world of your business processing. This is done through the use of Spring's MessageListenerAdapter class and IMessageConverters.