Run the configutil command with the syslogfacility option:
configutil -o logfile.service.syslogfacility -v value
where service is admin, pop, imap, imta, or http and value is user, mail, daemon, local0 to local7, or none.
Once the value is set, messages are logged to the syslog facility corresponding to the set value and all the other log file service options are ignored. When the option is not set or the value is none, logging uses the Messaging Server log files.