Box is right next to my desk at work, routing-wise it's inside the server room on the same IP subnet. I'm probably going to have to be the real source, as there are no exposed SMTP servers internal to our network at all. Box is not currently exposed to The Real WorldTM - but will be eventually, in theory. This is actually just the "demo box" - a VMWare instance that will eventually be The Real Thing.
Oh, and we're running Debian stable on the box currently.