rfc1939(c).txt

计算机网络的课件Courseware for computer networks

注意：除了STAT，LIST和UIDL的响应外，其它命令的响应均为"+OK"和 "-ERR"。响应后的所有文本将被客户略去。
9. POP3会话实例
S: <等待连接到TCP端口110>
C: <打开连接>
S: +OK POP3 server ready <[e-mail]>
C: APOP mrose c4c9334bac560ecc979e58001b3e22fb
S: +OK mrose's maildrop has 2 messages (320 octets)
C: STAT
S: +OK 2 320
C: LIST
S: +OK 2 messages (320 octets)
S: 1 120
S: 2 200
S: .
C: RETR 1
S: +OK 120 octets
S: <服务器发送信件1>
S: .
C: DELE 1
S: +OK message 1 deleted
C: RETR 2
S: +OK 200 octets
S: <服务器发送信件2>
S: .
C: DELE 2
S: +OK message 2 deleted
C: QUIT
S: +OK dewey POP3 server signing off (maildrop empty)
C: <关闭连接>
S: <等待下一次连接>
10. 消息格式
　　在会话过程中的消息格式都假定与Internet文本消息格式标准一致。应该注意的是，由于各个服务器对于换行符的处理不同，因此计数不一定相同。通常，在"确认"状态中，服务器能够以八进制计算信件的大小。例如，如果在打开储存邮件时服务器内部认定换行符代表一个字符，一般服务器在计算它时作为两个字符计。注意，以终止符开始的消息行不被计数两次，因为客户将在接收到多行响应后删除所有字节填充。
11. 安全性考虑
　　可以推测，使用APOP命令可以提供会话期间的保护。相应的，同时实现PASS和APOP命令的服务器只允许用户以一种方式访问；也就是说要么使用USER/PASS组合，要么使用APOP命令，不能同时使用两个。
而且，注意随着共享密钥长度的增加，解读的难度也就上升了。服务器要提供用户名时不给出任何响应，不给出任何暗示此用户名是否正确。而口令却在网络上显式传送；使用RETR和TOP命令在网络上显式传送信件。
12. 参考资料
   [RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
       821, USC/Information Sciences Institute, August 1982.

   [RFC822] Crocker, D., "Standard for the Format of ARPA-Internet Text
       Messages", STD 11, RFC 822, University of Delaware, August 1982.

   [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
       MIT Laboratory for Computer Science, April 1992.

   [RFC1730] Crispin, M., "Internet Message Access Protocol - Version
       4", RFC 1730, University of Washington, December 1994.

   [RFC1734] Myers, J., "POP3 AUTHentication command", RFC 1734,
       Carnegie Mellon, December 1994.

14. 致谢
   The POP family has a long and checkered history.  Although primarily
   a minor revision to RFC 1460, POP3 is based on the ideas presented in
   RFCs 918, 937, and 1081.

   In addition, Alfred Grimstad, Keith McCloghrie, and Neil Ostroff
   provided significant comments on the APOP command.
15. 作者地址
   John G. Myers
   Carnegie-Mellon University
   5000 Forbes Ave
   Pittsburgh, PA 15213

   EMail: [e-mail]

   Marshall T. Rose
   Dover Beach Consulting, Inc.
   420 Whisman Court
   Mountain View, CA  94043-2186

   EMail: [e-mail]
Appendix A. Differences from RFC 1725
   This memo is a revision to RFC 1725, a Draft Standard.  It makes the
   following changes from that document:

      - clarifies that command keywords are case insensitive.

      - specifies that servers must send "+OK" and "-ERR" in
        upper case.

      - specifies that the initial greeting is a positive response,
        instead of any string which should be a positive response.

      - clarifies behavior for unimplemented commands.

      - makes the USER and PASS commands optional.

      - clarified the set of possible responses to the USER command.

      - reverses the order of the examples in the USER and PASS
        commands, to reduce confusion.

      - clarifies that the PASS command may only be given immediately
        after a successful USER command.

      - clarified the persistence requirements of UIDs and added some
        implementation notes.

      - specifies a UID length limitation of one to 70 octets.

      - specifies a status indicator length limitation
        of 512 octets, including the CRLF.

      - clarifies that LIST with no arguments on an empty mailbox
        returns success.

      - adds a reference from the LIST command to the Message Format
        section

      - clarifies the behavior of QUIT upon failure

      - clarifies the security section to not imply the use of the
        USER command with the APOP command.

      - adds references to RFCs 1730 and 1734

      - clarifies the method by which a UA may enter mail into the
        transport system.

      - clarifies that the second argument to the TOP command is a
        number of lines.

      - changes the suggestion in the Security Considerations section
        for a server to not accept both PASS and APOP for a given user
        from a "must" to a "should".

      - adds a section on scaling and operational considerations

Appendix B. Command Index
       APOP .......................................................   15
       DELE .......................................................    8
       LIST .......................................................    6
       NOOP .......................................................    9
       PASS .......................................................   14
       QUIT .......................................................    5
       QUIT .......................................................   10
       RETR .......................................................    8
       RSET .......................................................    9
       STAT .......................................................    6
       TOP ........................................................   11
       UIDL .......................................................   12
       USER .......................................................   13



RFC1939  Post Office Protocol - Version 3                                   RFC1939-POP3协议

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