Location of the SBS 2011 POP3 Connector Log:
C:\Program Files\Windows Small Business Server\Logs\pop3connector\Pop3service.log
To create a new Pop3service log, you will need to stop the Windows SBS POP3 Connector service, rename the log file, and restart the service. A new log file will be created.
Link: http://blog.powerbiz.net.au/sbs-2008/sbs2008-and-sbs2011-log-file-locations/