1、Postfix搭建:详见
https://www.linuxdashen.com/ubuntu%E6%90%AD%E5%BB%BA%E7%AE%80%E6%98%93postfix%E9%82%AE%E7%AE%B1%E6%9C%8D%E5%8A%A1%E5%99%A8
2、DKIM安装:https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy
3、DNS配置:A记录、MX记录和两个TXT记录,配置一级域名时,可以把主机名、邮箱地址和域名写成一样的,不一样的认真看上面两篇博客,配置二级域名时,