rfc788.txt

RFC 相关的技术文档

            <d> ::= any one of the ten digits 0 through 9

            <s> ::= any one of <specials>

            <specials> ::= '<', '>', '(', ')', '\', ',', ';', ':', '@',
            '"', and the control characters (ASCII codes 0 through 37
            octal inclusive and 177 octal)

         Note that the backslash, '\', is a quote character, which is
         used to indicate that the next character is to be used
         literally (instead of its normal interpretation).  For example,
         "Joe\,Smith" could be used to indicate a single nine character
         user field with comma being the fourth character of the field.



Postel                                                         [Page 25]


                                                                        
November 1981                                                    RFC 788
Simple Mail Transfer Protocol                                           



         Hosts are generally known by names which are translated to
         addresses in each host.  Sometimes a host is not known to the
         translation function and communication is blocked.  To bypass
         this barrier two numeric forms are also allowed for host
         "names".  One form is a decimal integer prefixed by a pound
         sign, "#", which indicates the number is the address of the
         host.  Another form is four small decimal integers separated by
         dots and enclosed by brackets, e.g., "[123.255.37.2]", which
         indicates a 32-bit ARPA Internet Address in four 8-bit fields.

         The time stamp line and the return path line are formally
         defined as follows:

         <return-path-line> ::= "Return-Path:" <SP><reverse-path><CRLF>

         <time-stamp-line> ::= "Mail-From:" <SP> <stamp> <CRLF>

            <stamp> ::= [<ptcl>] <from-host> <this-host> <daytime>

            <ptcl> ::= <protocol> <SP> "host" <SP>

            <from-host> ::= <host> <SP>

            <this-host> ::= "received by" <SP> <host> <SP>

            <protocol> ::= "TCP" | "NCP" | "NITS" | "X25" | "INTERNET" |
                      "ARPANET"

               Note: INTERNET = TCP, ARPANET = NCP, and if the <ptcl> is
                         not present INTERNET is assumed.

            <daytime> ::= "at" <SP> <date> <SP> <time>

            <date> ::= <dd> "-" <mon> "-" <yy>

            <time> ::= <hh> ":" <mm> ":" <ss> "-" <zone>

            <dd> ::= the one or two decimal integer day of the month in
                      the range 1 to 31.

            <mon> ::= "JAN" | "FEB" | "MAR" | "APR" | "MAY" | "JUN" |
                      "JUL" | "AUG" | "SEP" | "OCT" | "NOV" | "DEC"

            <yy> ::= the two decimal integer year of the century in the
                      range 01 to 99.




[Page 26]                                                         Postel


                                                                        
RFC 788                                                    November 1981
                                           Simple Mail Transfer Protocol



            <hh> ::= the two decimal integer hour of the day in the
                      range 00 to 24.

            <mm> ::= the two decimal integer minute of the hour in the
                      range 00 to 59.

            <ss> ::= the two decimal integer second of the minute in the
                      range 00 to 59.

            <zone> ::= a time zone designator (as in [2]) or "UT" for
                      Universal Time (the default).

         Return Path Example:

            Return-Path: <@CHARLIE,@BAKER,JOE@ABLE>

         Mail From Example:

            Mail-From: ABC received by XYZ at 22-OCT-81 09:23:59-PDT

         




























Postel                                                         [Page 27]


                                                                        
November 1981                                                    RFC 788
Simple Mail Transfer Protocol                                           



   4.2.  SMTP REPLIES

      Replies to SMTP commands are devised to ensure the synchronization
      of requests and actions in the process of mail transfer, and to
      guarantee that the sender-SMTP always knows the state of the
      receiver-SMTP.  Every command must generate exactly one reply.

         The details of the command-reply sequence are made explicit in
         Section 5.3 on Sequencing and Section 5.4 State Diagrams.

      An SMTP reply consists of a three digit number (transmitted as
      three alphanumeric characters) followed by some text.  The number
      is intended for use by automata to determine what state to enter
      next; the text is meant for the human user.  It is intended that
      the three digits contain enough encoded information that the
      sender-SMTP need not examine the text and may either discard it or
      pass it on to the user, as appropriate.  In particular, the text
      may be receiver-dependent, so there are likely to be varying texts
      for each reply code.  A discussion of the theory of reply codes is
      given in the Appendix E.  Formally, a reply is defined to be the
      sequence:  a three-digit code, <SP>, one line of text, and <CRLF>,
      or a multiline reply (as defined in Appendix E).  Only the EXPN
      and HELP command are expected to result in multiline replies in
      normal circumstances, however multiline replies are allowed for
      any command.
























[Page 28]                                                         Postel


                                                                        
RFC 788                                                    November 1981
                                           Simple Mail Transfer Protocol



      4.2.1.  REPLY CODES BY FUNCTION GROUPS

         500 Syntax error, command unrecognized
            [This may include errors such as command line too long]
         501 Syntax error in parameters or arguments
         502 Command not implemented
         503 Bad sequence of commands
         504 Command parameter not implemented
          
         211 System status, or system help reply
         214 Help message
            [Information on how to use the receiver or the meaning of a
            particular non-standard command; this reply is useful only
            to the human user]
          
         220 <host> Service ready
         221 <host> Service closing transmission channel
         421 <host> Service not available, closing transmission channel
            [This may be a reply to any command if the service knows it
            must shut down]
          
         250 Requested mail action okay, completed
         251 User not local; will forward to <forward-path>
         450 Requested mail action not taken: mailbox unavailable
            [E.g., mailbox busy]
         550 Requested action not taken: mailbox unavailable
            [E.g., mailbox not found, no access]
         451 Requested action aborted: error in processing
         551 User not local; please try <forward-path>
         452 Requested action not taken: insufficient system storage
         552 Requested mail action aborted: exceeded storage allocation
         553 Requested action not taken: mailbox name not allowed
            [E.g., mailbox syntax incorrect]
         354 Start mail input; end with <CRLF>.<CRLF>
         554 Transaction failed
         













Postel                                                         [Page 29]


                                                                        
November 1981                                                    RFC 788
Simple Mail Transfer Protocol                                           



      4.2.2.  NUMERIC ORDER LIST OF REPLY CODES

         211 System status, or system help reply
         214 Help message
            [Information on how to use the receiver or the meaning of a
            particular non-standard command; this reply is useful only
            to the human user]
         220 <host> Service ready
         221 <host> Service closing transmission channel
         250 Requested mail action okay, completed
         251 User not local; will forward to <forward-path>
          
         354 Start mail input; end with <CRLF>.<CRLF>
          
         421 <host> Service not available, closing transmission channel
            [This may be a reply to any command if the service knows it
            must shut down]
         450 Requested mail action not taken: mailbox unavailable
            [E.g., mailbox busy]
         451 Requested action aborted: local error in processing
         452 Requested action not taken: insufficient system storage
          
         500 Syntax error, command unrecognized
            [This may include errors such as command line too long]
         501 Syntax error in parameters or arguments
         502 Command not implemented
         503 Bad sequence of commands
         504 Command parameter not implemented
         550 Requested action not taken: mailbox unavailable
            [E.g., mailbox not found, no access]
         551 User not local; please try <forward-path>
         552 Requested mail action aborted: exceeded storage allocation
         553 Requested action not taken: mailbox name not allowed
            [E.g., mailbox syntax incorrect]
         554 Transaction failed
         













[Page 30]                                                         Postel


                                                                        
RFC 788                                                    November 1981
                                           Simple Mail Transfer Protocol



   4.3.  SEQUENCING OF COMMANDS AND REPLIES

      The communication between the sender and receiver is intended to
      be an alternating dialogue, controlled by the sender.  As such,
      the sender issues a command and the receiver responds with a
      reply.  The sender must wait for this response before sending
      further commands.

      One important reply is the connection greeting.  Normally, a
      receiver will send a 220 "Awaiting input" reply when the
      connection is completed.  The sender should wait for this greeting
      message before sending any commands.

         Note: all the greeting type replies have the official name of
         the server host as the first word following the reply code.

            For example,

               220 <SP> USC-ISIF <SP> Service ready <CRLF>

      The table below lists alternative success and failure replies for
      each command.  These must be strictly adhered to; a receiver may
      substitute text in the replies, but the meaning and action implied
      by the code numbers and by the specific command reply sequence
      cannot be altered.

      COMMAND-REPLY SEQUENCES

         Each command is listed with its possible replies.  The prefixes
         used before the possible replies are "P" for preliminary (not
         used in SMTP), "I" for intermediate, "S" for success, "F" for
         failure, and "E" for error.  The 421 reply (service not
         available, closing transmission channel) may be given to any
         command if the SMTP-receiver knows it must shut down.  This
         listing forms the basis for the State Diagrams in Section 4.4.

            CONNECTION ESTABLISHMENT
               S: 220
               F: 421
            HELO
               S: 250
               E: 500, 501, 504, 421
            MAIL
               S: 250
               F: 552, 451, 452
               E: 500, 501, 421



Postel                                                         [Page 31]


                                                                        
November 1981                                                    RFC 788
Simple Mail Transfer Protocol                                           



            RCPT
               S: 250, 251
               F: 550, 551, 552, 553, 450, 451, 452
               E: 500, 501, 421
            DATA
               I: 354 -> data -> S: 250
                                 F: 552, 554, 451, 452
               F: 451, 554
               E: