接收邮件的程序,如果接收字符串的第一个字符为“+”表示服务器接收了来自客户端的请求命令

　　如果接到的第一个字符为“-”，则表示服务器认为来自客户端的请求是错误的。

　　如果会话状态正处于接收邮件，则不需要判断第一个字符。如果能够执行到这一步，表示发送给服务器的用户名已经通过服务器的验证，改变当前会话状态为发送密码阶段。

-Program receives the message, if the receiving string first character " +"　indicates that the server receives a request from the client request command from the client received the first character " -"　indicates that the server thinks wrong ' s. If session state is in receiving mail, you do not need to judge the first character. If you can perform this step, the user name sent to the server, change the current session state has passed the authentication of the server to send the password stage.