Exch2k7 Even 1035 - Inbound Authentication Failed

So shortly after upgrading our Exchange system to 2007, I started having trouble receiving emails from this one company. The following error would not go away and all other servers out there in the web that we sent mail to or received mail from had no problems. Even though Anonymous access was enabled on my Hub Transport server, the other server kept trying to authenticate with us.

Event Type: Error

Event Source: MSExchangeTransport

Event Category: SmtpReceive

Event ID: 1035

Date: 6/29/2007

Time: 11:17:42 AM

User: N/A

Computer: EXCHANGE2007

Description:

Inbound authentication failed with error LogonDenied for Receive connector Default EXCHANGE2007. The authentication mechanism is Gssapi. The source IP address of the client who tried to authenticate to Microsoft Exchange is .

So after many unsuccesful searches on the web, the microsoft newsgroups, etc I finally wound up using the empirical method and tried disabling some of the authentication methods. I restarted the Hub Transport service after each test to make sure the settings kicked in and voila the error went away. In the end, I wound up disabling the "Exchange Server authentication" and the "Integrated Windows authentication" options under Authentication under the Default Receive connector on my Hub Transport server. Since I don't have multiple Hub Transport servers this won't affect my environment for now and hopefully by the time I do it won't matter.