LOGLVL specifies the degree of detail to be written to the log file per the following table. It is ignored if LOGFILE is blank or not present, and it defaults to 1 (Errors only) if LOGLVL is not specified. The options are perhaps not completely self-explanatory, but the best way to understand them is just to experiment with a few sample messages and different settings. Typically you would just leave this set to 1 and check it periodically for error messages. Note that in the debug modes (4 and 5) the log file provides a rather graphic tutorial on how the SMTP protocol works, since it documents both the commands sent to the server and the responses received.