Centos6.x:
检查sendmail是否启动：
chkconfig –list | grep sendmail
若显示为空请通过以下命令设置sendmail自动启动：
service sendmail start
chkconfig –level 2345 sendmail on
Centos7.x:
检查sendmail是否启动：
systemctl list-units –type=service|grep sendmail
若显示为空请通过以下命令设置sendmail自动启动：
systemctl start sendmail.service
systemctl enable sendmail.service
