POP协议-Post Office Protocol,现在常用的是第三版，简称POP3,默认端口号为110。通过POP3,客户机登录服务器后，可以对自己的邮件进行删除或下载，下载后，电子邮件客户端软件就可以在本地对邮件进行处理，Windows操作系统默认安装的Outlook Express就采用这种工作方式。
　　实际上，收发邮件使用了两种协议，一种是TCP，用于收发数据；另一种是POP3，用于解析传送的命令。(POP protocol -Post Office Protocol, now commonly used is the third version, referred to as POP3, the default port number is 110. After POP3, the client is able to delete or download its own mail after logging on to the server. After downloading, the email client software can handle the mail locally, and the Outlook Express, which is installed by the Windows operating system by default, uses this mode of work.
Actually, there are two protocols for sending and receiving mail, one is TCP, which is used for sending and receiving data, the other is POP3, which is used to parse the command transmitted.)