About Message Queues

Microsoft Message Queues (MSMQ) is an interesting technology for asynchronous client-server applications. The general idea behind MSMQ is that clients communicate with servers via specific means called "queues". Contrary to MAPI, MSMQ interface is simple and very generic. It is simple to learn and easy to use. The power of MSMQ is that applications remain functional even when network connection between client and server is broken. Microsoft provides MSMQ middleware. You as a developer are responsible for implementing an MSMQ client, an MSMQ server, or both.

The simplicity of MSMQ is similar to named pipes. A few very generic operations are defined, such as sending a message to a queue and reading from a queue. However, for a named pipe application you need both client and server running and connected to each other. With MSMQ it is no longer necessary. The client may send a message to a queue and immediately continue with other tasks. Network connectivity is not required to exist, and the server is not required to run. Obviously, for any useful work done you still need the requests processed. This happens asynchronously when messages are first delivered to the server machine (when connection to the machine is established) and then when the server itself decides to process them. To some extent this is similar to exchange of paper letters between bureaucracies.

Microsoft has a lot of documentation about MSMQ. "MSMQ Guide" and "MSMQ Reference" are good starting points in MSDN Library.

MSMQ enter MAPI and Exchange world with two items: the MSMQ MAPI transport and the MSMQ Exchange connector. These two components allow to establish communication between a MAPI application such as the Outlook client and an MSMQ application. If you plan to use MS Exchange server - you need the connector, otherwise MAPI transport would be just fine. Both components are provided by Microsoft as parts of MSMQ server installation. The beauty of this is that via this mechanism you may obtain easy connectivity to Exchange and MAPI clients without investing a lot of time learning MAPI.

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