sendmail
(1)配置dns主配置文件
   并添加相应的MX记录
(2)vim /etc/sysconfig/network
       HOSTNAME=mail.abc.com
(3)rpm -ivh sendmail-cf---------
(4)cd /etc/mail
   vim sendmail.mc
       116:改Addr=0.0.0.0
       52：TRUST_AUTH_MECH------------
       53：define---------------------
(5)vim access
        添加：
        192.168.1.0              REALY
(6)makemap hash access.db < access
   m4 sendmail.mc > sendmail.cf
(7)vim local-host-names
       添加:
       abc.com
(8)groupadd mails
   useradd lala -s /sbin/nologin
   passwd lala
   useradd haha -s /sbin/nologin
   passwd haha
(9)newaliases
(10)/etc/init.d/saslauthd restart
    /etc/init.d/sendmail restart
    此时sendmail能发邮件，但是不能接收邮件！
    因为还没有安装pop3
(11)rpm -ivh perl-DBI-----
    rpm -ivh mysql-5----
    rpm -ivh dovecot-------
(12)vim /etc/dovecot.conf
        20:protocols = -------
    service dovecot start