Standard Exchange Message Tracking from EMC Toolbox is a useful tool and often helps to diagnose message delivery issues. However if message is rejected at Hub Transport level it will not be logged in Message Tracking logs. To trace such messages you need to enable Receive Connector Logging.

Open Exchange Management Console > Server Configuration > Hub Transport > [Receive Connector] > Properties > General > Protocol Logging Level
Change the level from None to Verbose.

By default logs will be saved in :

C:\Program Files\Microsoft\Exchange Server\TransportRoles\Logs\ProtocolLog\SmtpReceive

Make sure you disable logging after troubleshooting is finished.

If you have Edge Transport Server you will need to enable Protocol Logging on Edge Transport Receive Connector as this will be the first place where messages hit your network.

Exchange 2007
Windows Small Business Server (SBS) 2008