A server running Microsoft Message Queue (MSMQ) Server that supports dynamic routing and intermediate store-and-forward message queuing. MSMQ Routing Servers enable computers using different network protocols to communicate.
MSMQ Routing Servers do not contain copies of the primary site controller (PSC) or primary enterprise controller (PEC) database. Before you can install any MSMQ Routing Servers in your network, you must first install a PEC.
Since every PEC, PSC, and backup site controller (BSC) functions as an MSMQ Routing Server, the number of additional MSMQ Routing Servers you need depends on your MSMQ connectivity needs, namely
Be sure to install enough MSMQ Routing Servers so that messages can reach their target queues through different servers.