先搭建一个DNS服务器解析邮件
yum -y install /mnt/Packages/sendmail-*
cd /etc/mail
vi access //设置邮件服务器使用权限
Connect:abc.com RELAY
Connect:172.16.5.116 RELAY
makemap hash access.db < access
vi /etc/mail/local-host-names //设置sendmail的本地主机名
添加abc.com和mail.abc.com
vi sendmail.mc
第116行127.0.0.1改0.0.0.0
m4 sendmail.mc > sendmail.cf
service sendmail restart
useradd mail1
useradd mail2 //创建两个用户测试
telnet 172.16.5.116 25
