Your mail service logs most error messages by using the syslogd program. By default, the syslogd program sends these messages to a system that is called loghost, which is specified in the /etc/hosts file. You can define loghost to hold all logs for an entire NIS domain. If no loghost is specified, error messages from syslogd are not reported.
The /etc/syslog.conf file controls where the syslogd program forwards messages. You can change the default configuration by editing the /etc/syslog.conf file. You must restart the syslog daemon for any changes to become active. To gather information about mail, you can add the following selections to the file.
mail.alert – Messages about conditions that should be fixed now
mail.crit – Critical messages
mail.warning – Warning messages
mail.notice – Messages that are not errors, but might need attention
mail.info – Informational messages
mail.debug – Debugging messages
The following entry in the /etc/syslog.conf file sends a copy of all critical, informational, and debug messages to /var/log/syslog.
mail.crit;mail.info;mail.debug /var/log/syslog
Each line in the system log contains a timestamp, the name of the system that generated the line, and a message. The syslog file can log a large amount of information.
The log is arranged in a succession of levels. At the lowest level, only unusual occurrences are logged. At the highest level, even the most mundane and uninteresting events are recorded. As a convention, log levels under 10 are considered “useful.” Log levels that are higher than 10 are usually used for debugging. See Customizing System Message Logging in Troubleshooting System Administration Issues in Oracle Solaris 11.2 for information about loghost and the syslogd program.