Here is the location for the smtp receive connector
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\ProtocolLog\SmtpReceive
Location for smtp send connector
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\ProtocolLog\SmtpSend
Location for connectivity log
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\Connectivity
Location for message tracking logs
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\MessageTracking
Location for the routing logs
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\Routing
Instructions to configure the location of the logs can be found here:
http://technet.microsoft.com/en-us/library/aa998617.aspx