1、 安装 Postfix：

# yum update && yum install postfix

2、 启动服务并启用开机自动启动：

# systemctl start postfix
# systemctl enable postfix

[root@testserver ~]# postconf -e inet_interfaces=loopback-only
[root@testserver ~]# postconf -e mynetworks="127.0.0.0/8"
[root@testserver ~]# postconf -e myorigin=ldap.example.com
[root@testserver ~]# postconf -e "mydestination="
[root@testserver ~]# postconf -e "local_transport=error: local delivery disabled"

[root@testserver ~]# systemctl restart postfix.service
[root@testserver ~]# firewall-cmd --permanent --add-service=smtp
[root@testserver ~]# firewall-cmd --reload