Is $config['smtp_log'] set to false in your config?
It looks like the default for this is to be true so it would need to be set false in the config rather than commented out like other logging.
Steve.
Thank you very much, that solved it. I did not know about this switch but found it afterwards in defaults.inc.php set to true. Setting to false in config.inc.php overrides this and shuts smtp-logging completely. georg