一/测试SMTP发送邮件
[root@mail ~]# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 mail.zpp.com ESMTP Postfix
helo localhost   //宣告客户端地址
250 mail.zpp.com
mail from:zpp001@zpp.com   //告知服务器发件人地址
250 2.1.0 Ok
rcpt to:zpp002@zpp.com     //告知服务器收件人地址
250 2.1.5 Ok
Data    //告知服务器要传送数据了
354 End data with <CR><LF>.<CR><LF>
subject:I Love You!    //主题
hello!
You are my super star! he he he !    //邮件内容以点结束
.
250 2.0.0 Ok: queued as 27ECCE01ED
Quit     //退出
221 2.0.0 Bye
Connection closed by foreign host.


二/测试POP3接收邮件
[root@mail ~]# telnet localhost 110
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
+OK Dovecot ready.
user zpp002  //使用邮件用户“zpp002”登录
+OK
pass 123.com  //键入密码123.com
+OK Logged in.
List    //查看邮件列表
+OK 1 messages:
1 485
.
retr 1   //收取并查看第一封邮件内容
+OK 485 octets
Return-Path: <zpp001@zpp.com>
X-Original-To: zpp002@zpp.com
Delivered-To: zpp002@zpp.com
Received: from localhost (localhost.localdomain [127.0.0.1])
        by mail.zpp.com (Postfix) with SMTP id 27ECCE01ED
        for <zpp002@zpp.com>; Thu, 28 Jan 2021 03:57:40 +0800 (CST)
subject:I Love You!
Message-Id: <20210127195752.27ECCE01ED@mail.zpp.com>
Date: Thu, 28 Jan 2021 03:57:40 +0800 (CST)
From: zpp001@zpp.com
To: undisclosed-recipients:;
hello!
You are my super star! he he he !
.
quit
+OK Logging out.
Connection closed by foreign host.