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.
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 System Administration Guide: Advanced Administration for information about loghost and the syslogd program.