POP3协议要点 ,更详细的信息可以查看 RFC1939
(1) POP3命令由一个命令和一些参数组成。所有命令以一个CRLF对结束
(2) 命令和参数由可打印的ASCII字符组成,它们之间由空格间隔
(3) POP3响应由一个状态码和一个可能跟有附加信息的命令组成。所有响应也是由CRLF对结束
(4) 有两种状态码,"确定" ("+OK")和"失败" ("-ERR")。
(5) 当所有信息发送结束时,发送最后一行,包括一个结束字符(十进制码46,也就是".")和一个CRLF对。
(6) 在POP3协议中有三种状态,认可状态,处理状态,和更新状态。
当客户机与服务器建立联系时,一旦客户机提供了自己身份并成功确认,即由认可状态转入处理状态,在完成相应的操作后客户机发出QUIT命令,则进入更新状态,更新之后最后重返认可状态。如下图
等待连接 身份确认 QUIT命令
—— |认可|————— |处理|——————|更新|
|__________________________________|
重返认可状态
一个最小的,成功的Client-Server会话过程
POP3 Client POP3 Server
Socket() listen()
Connect() -------------------------------> accept()
<------------------------------ +OK 发送确认消息 (进入"确认"状态)
发送USER命令------------------------------>
<----------------------------- +OK 发送确认消息
发送PASS命令------------------------------>
<----------------------------- +OK 发送确认消息 (进入"操作"状态)
发送QUIT命令------------------------------>
<----------------------------- +OK 发送确认消息 (进入"更新"状态)
如果客户在"确认"状态下发送QUIT后,会话并不进入"更新"状态
可以在命令行(cmd.exe)里测试一下:
c:\telnet pop3.163.com 110 //连接网易的邮件服务器
+OK coremail .... //服务器返回+OK
USER 'yourusername' //客户端发出用户名,可能在yourusername上需要一对单引号
PASS 'yourpassword' //客户端发出密码,可能在yourpassword上需要一对单引号
+OK mm nn // 返回邮件数和大小
STAT //得到邮箱的状态
+OK xxx xxx // 返回邮件数和大小
客户可以发出的命令列表以及含义,源自ChinaUnix
命令 参数 状态 描述
------------------------------------------------------------------------------------------------------------------------------
USER username 认可 此命令与下面的pass命令若成功,将导致状态转换
PASS password 认可
APOP Name,Digest 认可 Digest是MD5消息摘要,windows系统多不支持
------------------------------------------ -----------------------------------------------------------------------------------
STAT None 处理 请求服务器发回关于邮箱的统计资料,如邮件总数和总字节数
UIDL [Msg#] 处理 返回邮件的唯一标识符,POP3会话的每个标识符都将是唯一的
LIST [Msg#] 处理 返回邮件数量和每个邮件的大小
RETR [Msg#] 处理 返回由参数标识的邮件的全部文本
DELE [Msg#] 处理 服务器将由参数标识的邮件标记为删除,由quit命令执行
RSET None 处理 服务器将重置所有标记为删除的邮件,用于撤消DELE命令
TOP [Msg#] 处理 服务器将返回由参数标识的邮件前n行内容,n必须是正整数
NOOP None 处理 服务器返回一个肯定的响应
------------------------------------------------------------------------------------------------------------------------------
QUIT None 更新
Foxmail 和 Outlook 使用 pop3时的异同 源自LinuxForum.net
假定服务器上有三封邮件等待客户机接收。用foxmail与OE的不同之处在于foxmail每收一封标记删除一封,而Outlook则等全部接收完后再全部标记为删除最后执行quit命令。
Foxmail OutLook
-------------------------------------------
RETR 1 RETR 1
DELE 1 RETR 2
RETR 2 RETR 3
DELE 2 DELE 1
RETR 3 DELE 2
DELE 3 DELE 3
QUIT QUIT
-------------------------------------------
简单的C#代码就可以实现pop3邮箱的监控
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上面的代码完成了监控的基本功能,但是还不够,首先缺少异常处理,比如在socket.connect() 那里,连接失败了怎么办?其次,如果你想把邮件收到本地,那么字符的编码就成了问题,尤其是汉字的处理比较麻烦,详细的情况可以查看 RFC822 .你可以完善基本的代码,实现本地POP3收信了.
现在可以测试一下:
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