MSMQ-based applications can send messages to and receive messages from other enterprises. This allows MSMQ-based applications to communicate over the Internet.
Note MSMQ communicates over TCP port 1801, registered with the Internet Assigned Numbers Authority (IANA). MSMQ-based applications can communicate over properly configured firewalls that allow communication over that port.
For more information on writing MSMQ-based applications that send messages between enterprises, see the MSMQ SDK.