As the log server may receive quite a large number of log messages from clients (depending on the number of clients and their threshold settings), client messages are treated specially and by default are only logged to facilities suitable for bulk logging: console, log file, relational database (if enabled), and external (if enabled).
To override this behavior, you can set the option 
      UseClientSeverity=
      yes in the 
      [Misc] section of the configuration file.
      In that case, the client message severity is used, and client
      messages are treated just like local messages (i.e. like
      those from the server itself).
If you also want to filter by message class, there is
      also an option 
      UseClientClass=
      yes 
All client messages are recorded in the main log file
      by default. However, it is possible to use separate log files
      for individual clients. This can be enabled with 
      UseSeparateLogs=
      yes/no in the 
      Misc section of the server configuration
      file. No locking will be performed for such separate client
      log files (only one instance of the server can listen on the
      TCP port, thus there will be no concurrent access).