Microsoft Message Queuing

Microsoft Message Queuing or MSMQ is a message queue implementation developed by Microsoft and deployed in its Windows Server operating systems since Windows NT 4 and Windows 95. Windows Server 2016 and Windows 10 also includes this component. In addition to its mainstream server platform support, MSMQ has been incorporated into Microsoft Embedded platforms since 1999 and the release of Windows CE 3.0.

MSMQ is essentially a messaging protocol that allows applications running on separate servers/processes to communicate in a failsafe manner. A queue is a temporary storage location from which messages can be sent and received reliably, as and when conditions permit. This enables communication across networks and between computers, running Windows, which may not always be connected. By contrast, sockets and other network protocols assume that direct connections always exist.

MSMQ has been available to developers on Microsoft platforms since 1997, and has commonly been used in enterprise software built with Visual Studio, both in the native pre-.NET incarnation (version 5 and 6), and in Visual Studio .NET. Microsoft also has incorporated MSMQ in its messaging technology framework, Windows Communication Foundation (WCF). Under WCF, MSMQ can be used for providing secure, reliable transport with a unified programming model compatible with other communications standards.

MSMQ is responsible for reliably delivering messages between applications inside and outside the enterprise. MSMQ ensures reliable delivery by placing messages that fail to reach their intended destination in a queue and then resending them once the destination is reachable. It also supports security and priority based messaging. Dead letter queues can be created for looking at messages which timed out or failed for other reasons.

...
Wikipedia