Edit the MTA Option file.
A value of 0 disables generation of the syslog notices. A non-zero value enables generation of the syslog notices, with the absolute value controlling the syslog priority and facility mask. (Positive values mean syslog notices and the regular mail.log* entries; negative values, which are not recommended, mean syslog notices only, disabling the regular mail.log* entries. A value of 0 is the default and indicates that syslog (event log) logging is not performed.