There are cases when you need to allow unauthenticated relaying for specific hosts or network devices in Exchange Server 2007. Typical examples are software packages (like accounting software) or network printers, scanners etc.
Exchange Server 2007 allows authenticated relaying, so if your device or application can authenticate, then this is the recommended approach.
On the other hand, if you don’t have a choice due to software or hardware limitations, your other option is allowing anonymous relay on Exchange Server 2007. As you do not want to turn the Exchange server into an open relay, you have to configure a new connector and restrict anonymous relay based on the source of incoming messages.

In the following Screencast, we will demonstrate how to allow anonymous relay on a receive connector for a specific IP address – a host which is running an accounting application.