I have a SMTP gateway (192.168.50.3) that cannot relay email to my Exchange SMTP Virtual Server (192.168.50.2). My Exchange Virtual Server does not allow for anonymous authentication. I do have my the SMTP gateway listed in the list of computers that are allowed to relay through my Exchange Virtual Server, but I also have "Allow all computers that successful authenticate to relay, regardless of the list above" check marked. The Exchange Virtual Server allows any computer to connect to it.
When I allow anonymous authentication, the SMTP gateway can relay messages to the Exchange SMTP Virtual Server just fine. How do I setup the Exchange SMTP Virtual Server to not allow anonymous authentication but allow the SMTP gateway to relay messages?