sendmail (邮件服务器)
MUA (Mail User Agent) 邮件用户代理
MTA (Mail Transfer Agent) 邮件传输代理
MDA (Mail Dilivery Agent) 邮件接收发送代理
SMTP (Simple Message Transfer Potocol) 25号端口
POP3 ( Post Office Protocol) 110号端口
安装：
挂载第二张光盘
rpm -ivh sendmail-8.13.1-2.i386.rpm
rpm -ivh m4-1.4-16.i386.rpm
挂载第四张光盘
rpm -ivh sendmail-cf-8.13.1-2.i386.rpm
rpm -ivh sendmail-doc-8.13.1-2.i386.rpm
rpm -ivh sendmail-devel-8.13.1-2.i386.rpm
vi /etc/mail/local-host-names
增加本地域和主机的FQDN
service sendmail restart
说明：
Sendmail.mc是sendmail的主配置文件，它决定了sendmail的属性。Sendmail.mc是由若干个宏代码构成，可以通过m4工具编译成sendmail.cf
vi /etc/mail/sendmail.mc
修改：DAEMON_OPTIONS ('port=smtp,Addr=127.0.0.1,Name=MTA')dnl
为： DAEMON_OPTIONS ('port=smtp,Addr=0.0.0.0,Name=MTA')dnl
转换文件：
m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
安装邮局服务：
挂载第四张光盘
rpm -ivh dovecot-0.99.11-2.EL4.i386.rpm
vi /etc/dovecot.conf
#protocols = imap imaps
改为：
protocols = imap imaps pop3 pop3s
service dovecot restart
netstat -tnlp | grep 110
PS:
DNS中要写入
IN MX 10 baidu.com.
mail IN A 192.168.8.8
smtp IN CNAME mail
pop3 IN CNAME mail
发送邮件：
mail user1
subject:hello
welcome to here
ctrl+DD 发送邮件