PHP自带函数无法发送邮件解决

教程说明

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