POP3 logging is not enabled by default in Exchange 2007. To enable it, edit the C:\Program Files\Microsoft\Exchange Server\ClientAccess\PopImap\Microsoft.Exchange.Pop3.exe.config file.
Under appSettings, change
<add key=”ProtocolLog” value=”false” />
to
<add key=”ProtocolLog” value=”true” />
and restart the Microsoft Exchange POP3 service. You can restart it in services.msc or run the following command from the Exchange Management Console:
Restart-service MSExchangePOP3
Log files will be created in your C:\Program Files\Microsoft\Exchange Server\Logging\Pop3 folder.