邮件接收处理 这个例子中只需要编写客户端程序，而不需要编写服务器端程序即可正常运行。我们重点关心的是如何利用同步TCP发送和接收数据。 -Receiving and processing the message only need to write this example client, without the need to write server-side program to work correctly. The focus of our concern is how to