I'm running Windows Small Business Server 2003 with Exchange 2003. We only have the one server. The remote host IP shown is not ours or our ISP's.
Yesterday I had two occurrences of the following error logged:
This is an SMTP protocol error log for virtual server ID 1, connection #8. The remote host "184.108.40.206", responded to the SMTP command "xexch50" with "504 Need to authenticate first ". The full command sent was "XEXCH50 2536 2 ". This will probably cause the connection to fail. For more information, click http://www.microsoft.com/contentredirect.asp
I followed the MS KB article 843106. On our side it seems things are configured as outlined.
If there is any other information I can provide to help diagnose please let me know.
PS: I'm not an Exchange expert. :-)