I just stumbled over a nice cool online tool from the Exchange Team over at http://blog.unifiedcommunications.eu/
It seems that the Microsoft Exchange Team is working on a online tool to test Exchange Internet based services (ActiveSync, Outlook Anywhere, Autodiscover & SMTP) The tool is still Prototype, and i have found no public references to it yet. So it should be used as-is.
The Microsoft Exchange Server Remote Connectivity Analyzer (nice name by the way) can help you test and troubleshoot you public configuration (Public DNS & Firewall)
To use the tool, you must enter username and password to complete the test. It is highly recommended that you create a temporary user for this test, and delete it after you complete the test.
I just checked the WhoIs database with this result:
(… So it is Microsoft.)