From a newsgroup post: "Try this procedure from Microsoft Exchange Message Reference (BORK):
If a successful connection was made between client and server, and problems are encountered, the conversion can be viewed by using protocol logging. By default, protocol logging is not enabled, but the administrator can select conversions to be logged. There are two values for protocol logging: POP3 Protocol Log Path, and POP3 Protocol Logging Level. By default, the conversions are logged in the \Mdbdata directory. The path for default logging is stored in:
To enable logging, modify the registry key:
Set the value to 0, 1, or 4, depending on whether no, minimum, or maximum logging is desired. If these entries are changed, the information store must be restarted before the new values will take effect."