本节中将概要的介绍下pop3和ipops服务器的简单配置，以及Linux下抓包工具的使用，国内用户普遍喜欢用pop3协议收取邮件，这非常的不安全，所以本节中也将概要的介绍下ipops服务器的配置，生产环境中配置ipop3服务器需要将pem格式的证书给CA签名才能被其他用户所信任和使用，pop3，imap协议默认使用TCP的110和143端口，ipops和imaps协议默认则使用TCP的993和995端口，邮件服务使用的账号是系统账户，所以安全性相当的重要，这也是RHCE的重点…
[root@server ~]# yum -y install dovecot.i386 //安装dovecot软件包，启动服务，设定下次开启自动启动，查看端口
[root@server ~]# service dovecot start
Starting Dovecot Imap: [ OK ]
[root@server ~]# chkconfig dovecot on
[root@server ~]# netstat -ntpl |grep -E '110|143|993|995+'
tcp 0 0 :::993 :::* LISTEN 4652/dovecot
tcp 0 0 :::995 :::* LISTEN 4652/dovecot
tcp 0 0 :::110 :::* LISTEN 4652/dovecot
tcp 0 0 :::143 :::* LISTEN 4652/dovecot
[root@server ~]# useradd test //新建一个系统账户用于测试
[root@server ~]# echo "test" |passwd --stdin test
Changing password for user test.
passwd: all authentication tokens updated successfully.
[root@server ~]# yum -y install wireshark.i386 //安装抓包工具wireshark
[root@server ~]# ifconfig eth1 |grep 'inet addr' //查看本机IP地址
inet addr:192.168.100.254 Bcast:192.168.100.255 Mask:255.255.255.0
[root@client ~]# nmap 192.168.100.254 //在客户端使用nmap扫描服务器端开启的端口
Starting Nmap 4.11 ( ) at 2010-03-24 00:00 EDT
Interesting ports on 192.168.100.254:
Not shown: 1667 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
25/tcp open smtp
53/tcp open domain
110/tcp open pop3
111/tcp open rpcbind
143/tcp open imap
763/tcp open cycleserv
784/tcp open unknown
796/tcp open unknown
993/tcp open imaps
995/tcp open pop3s
2049/tcp open nfs
MAC Address: 00:0C:29:0C:7C:4E (VMware)
Nmap finished: 1 IP address (1 host up) scanned in 23.250 seconds
[root@client ~]# telnet 192.168.100.254 110 //客户端使用telnet登陆POP3服务器
Trying 192.168.100.254...
Connected to 192.168.100.254 (192.168.100.254).
Escape character is '^]'.
+OK Dovecot ready.
user test
+OK
pass test
+OK Logged in.
quit
+OK Logging out.
Connection closed by foreign host.