/var/log/maillog会记录包含系统上运行的邮件服务器的日志信息，比如记录 postfix 或 sendmail 运行时的日志信息
[root@localhost ~]# tail /var/log/maillog Dec 18 04:00:05 localhost postfix/sendmail[2670]: warning: valid_hostname: numeric hostname: 231.133.13 Dec 18 04:00:05 localhost postfix/sendmail[2670]: fatal: file /etc/postfix/main.cf: parameter mydomain: bad parameter value: 231.133.13 Dec 19 04:00:06 localhost postfix/sendmail[9331]: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol Dec 19 04:00:06 localhost postfix/sendmail[9331]: warning: inet_protocols: configuring for IPv4 support only Dec 19 04:00:06 localhost postfix/sendmail[9331]: warning: valid_hostname: numeric hostname: 231.133.13
可以分为几个字段来描述这些事件信息：
1. 事件的日期和时间
2. 事件的来源主机
3. 产生这个事件的程序[进程号]
4. 实际的日志信息