rfc821_smtp.txt

邮件编码格式说明。

            others (for example, due to mailbox space allocation
            problems).  In such a situation, the response to the DATA
            command must be an OK reply.  But, the receiver-SMTP must
            compose and send an "undeliverable mail" notification
            message to the originator of the message.  Either a single
            notification which lists all of the recipients that failed
            to get the message, or separate notification messages must
            be sent for each failed recipient (see Example 7).  All
            undeliverable mail notification messages are sent using the
            MAIL command (even if they result from processing a SEND,
            SOML, or SAML command).


     -------------------------------------------------------------

            Example of Return Path and Received Time Stamps

      Return-Path: <@GHI.ARPA,@DEF.ARPA,@ABC.ARPA:[e-mail]>   
      Received: from GHI.ARPA by JKL.ARPA ; 27 Oct 81 15:27:39 PST
      Received: from DEF.ARPA by GHI.ARPA ; 27 Oct 81 15:15:13 PST
      Received: from ABC.ARPA by DEF.ARPA ; 27 Oct 81 15:01:59 PST
      Date: 27 Oct 81 15:01:01 PST                                
      From: [e-mail]                                          
      Subject: Improved Mailing System Installed                  
      To: [e-mail]                                            
                                    
      This is to inform you that ...                              

                               Example 8

     -------------------------------------------------------------

         SEND (SEND)

            This command is used to initiate a mail transaction in which
            the mail data is delivered to one or more terminals.  The
            argument field contains a reverse-path.  This command is
            successful if the message is delivered to a terminal.

            The reverse-path consists of an optional list of hosts and
            the sender mailbox.  When the list of hosts is present, it
            is a "reverse" source route and indicates that the mail was
            relayed through each host on the list (the first host in the
            list was the most recent relay).  This list is used as a
            source route to return non-delivery notices to the sender.
            As each relay host adds itself to the beginning of the list,
            it must use its name as known in the IPCE to which it is
            relaying the mail rather than the IPCE from which the mail
            came (if they are different).

            This command clears the reverse-path buffer, the
            forward-path buffer, and the mail data buffer; and inserts
            the reverse-path information from this command into the
            reverse-path buffer.

         SEND OR MAIL (SOML)

            This command is used to initiate a mail transaction in which
            the mail data is delivered to one or more terminals or
            mailboxes. For each recipient the mail data is delivered to
            the recipient's terminal if the recipient is active on the
            host (and accepting terminal messages), otherwise to the
            recipient's mailbox.  The argument field contains a
            reverse-path.  This command is successful if the message is
            delivered to a terminal or the mailbox.

            The reverse-path consists of an optional list of hosts and
            the sender mailbox.  When the list of hosts is present, it
            is a "reverse" source route and indicates that the mail was
            relayed through each host on the list (the first host in the
            list was the most recent relay).  This list is used as a
            source route to return non-delivery notices to the sender.
            As each relay host adds itself to the beginning of the list,
            it must use its name as known in the IPCE to which it is
            relaying the mail rather than the IPCE from which the mail
            came (if they are different).

            This command clears the reverse-path buffer, the
            forward-path buffer, and the mail data buffer; and inserts
            the reverse-path information from this command into the
            reverse-path buffer.

         SEND AND MAIL (SAML)

            This command is used to initiate a mail transaction in which
            the mail data is delivered to one or more terminals and
            mailboxes. For each recipient the mail data is delivered to
            the recipient's terminal if the recipient is active on the
            host (and accepting terminal messages), and for all
            recipients to the recipient's mailbox.  The argument field
            contains a reverse-path.  This command is successful if the
            message is delivered to the mailbox.

            The reverse-path consists of an optional list of hosts and
            the sender mailbox.  When the list of hosts is present, it
            is a "reverse" source route and indicates that the mail was
            relayed through each host on the list (the first host in the
            list was the most recent relay).  This list is used as a
            source route to return non-delivery notices to the sender.
            As each relay host adds itself to the beginning of the list,
            it must use its name as known in the IPCE to which it is
            relaying the mail rather than the IPCE from which the mail
            came (if they are different).

            This command clears the reverse-path buffer, the
            forward-path buffer, and the mail data buffer; and inserts
            the reverse-path information from this command into the
            reverse-path buffer.

         RESET (RSET)

            This command specifies that the current mail transaction is
            to be aborted.  Any stored sender, recipients, and mail data
            must be discarded, and all buffers and state tables cleared.
            The receiver must send an OK reply.

         VERIFY (VRFY)

            This command asks the receiver to confirm that the argument
            identifies a user.  If it is a user name, the full name of
            the user (if known) and the fully specified mailbox are
            returned.

            This command has no effect on any of the reverse-path
            buffer, the forward-path buffer, or the mail data buffer.

         EXPAND (EXPN)

            This command asks the receiver to confirm that the argument
            identifies a mailing list, and if so, to return the
            membership of that list.  The full name of the users (if
            known) and the fully specified mailboxes are returned in a
            multiline reply.

            This command has no effect on any of the reverse-path
            buffer, the forward-path buffer, or the mail data buffer.

         HELP (HELP)

            This command causes the receiver to send helpful information
            to the sender of the HELP command.  The command may take an
            argument (e.g., any command name) and return more specific
            information as a response.

            This command has no effect on any of the reverse-path
            buffer, the forward-path buffer, or the mail data buffer.

         NOOP (NOOP)

            This command does not affect any parameters or previously
            entered commands.  It specifies no action other than that
            the receiver send an OK reply.

            This command has no effect on any of the reverse-path
            buffer, the forward-path buffer, or the mail data buffer.

         QUIT (QUIT)

            This command specifies that the receiver must send an OK
            reply, and then close the transmission channel.

            The receiver should not close the transmission channel until
            it receives and replies to a QUIT command (even if there was
            an error).  The sender should not close the transmission
            channel until it send a QUIT command and receives the reply
            (even if there was an error response to a previous command).
            If the connection is closed prematurely the receiver should
            act as if a RSET command had been received (canceling any
            pending transaction, but not undoing any previously
            completed transaction), the sender should act as if the
            command or transaction in progress had received a temporary
            error (4xx).

         TURN (TURN)

            This command specifies that the receiver must either (1)
            send an OK reply and then take on the role of the
            sender-SMTP, or (2) send a refusal reply and retain the role
            of the receiver-SMTP.

            If program-A is currently the sender-SMTP and it sends the
            TURN command and receives an OK reply (250) then program-A
            becomes the receiver-SMTP.  Program-A is then in the initial
            state as if the transmission channel just opened, and it
            then sends the 220 service ready greeting.

            If program-B is currently the receiver-SMTP and it receives
            the TURN command and sends an OK reply (250) then program-B
            becomes the sender-SMTP.  Program-B is then in the initial
            state as if the transmission channel just opened, and it
            then expects to receive the 220 service ready greeting.

            To refuse to change roles the receiver sends the 502 reply.

         There are restrictions on the order in which these command may
         be used.

            The first command in a session must be the HELO command.
            The HELO command may be used later in a session as well.  If
            the HELO command argument is not acceptable a 501 failure
            reply must be returned and the receiver-SMTP must stay in
            the same state.

            The NOOP, HELP, EXPN, and VRFY commands can be used at any
            time during a session.

            The MAIL, SEND, SOML, or SAML commands begin a mail
            transaction.  Once started a mail transaction consists of
            one of the transaction beginning commands, one or more RCPT
            commands, and a DATA command, in that order.  A mail
            transaction may be aborted by the RSET command.  There may
            be zero or more transactions in a session.

            If the transaction beginning command argument is not
            acceptable a 501 failure reply must be returned and the
            receiver-SMTP must stay in the same state.  If the commands
            in a transaction are out of order a 503 failure reply must
            be returned and the receiver-SMTP must stay in the same
            state.

            The last command in a session must be the QUIT command.  The
            QUIT command can not be used at any other time in a session.

      4.1.2.  COMMAND SYNTAX

         The commands consist of a command code followed by an argument
         field.  Command codes are four alphabetic characters.  Upper
         and lower case alphabetic characters are to be treated
         identically.  Thus, any of the following may represent the mail
         command:

            MAIL    Mail    mail    MaIl    mAIl

         This also applies to any symbols representing parameter values,
         such as "TO" or "to" for the forward-path.  Command codes and
         the argument fields are separated by one or more spaces.
         However, within the reverse-path and forward-path arguments
         case is important.  In particular, in some hosts the user
         "smith" is different from the user "Smith".

         The argument field consists of a variable length character
         string ending with the character sequence <CRLF>.  The receiver
         is to take no action until this sequence is received.

         Square brackets denote an optional argument field.  If the
         option is not taken, the appropriate default is implied.


         The following are the SMTP commands:

            HELO <SP> <domain> <CRLF>

            MAIL <SP> FROM:<reverse-path> <CRLF>

            RCPT <SP> TO:<forward-path> <CRLF>

            DATA <CRLF>

            RSET <CRLF>

            SEND <SP> FROM:<reverse-path> <CRLF>

            SOML <SP> FROM:<reverse-path> <CRLF>

            SAML <SP> FROM:<reverse-path> <CRLF>

            VRFY <SP> <string> <CRLF>

            EXPN <SP> <string> <CRLF>

            HELP [<SP> <string>] <CRLF>

            NOOP <CRLF>

            QUIT <CRLF>

            TURN <CRLF>





         The syntax of the above argument fields (using BNF notation
         where applicable) is given below.  The "..." notation indicates
         that a field may be repeated one or more times.

            <reverse-path> ::= <path>

            <forward-path> ::= <path>

            <path> ::= "<" [ <a-d-l> ":" ] <mailbox> ">"

            <a-d-l> ::= <at-domain> | <at-domain> "," <a-d-l>

            <at-domain> ::= "@" <domain>

            <domain> ::=  <element> | <element> "." <domain>

            <element> ::= <name> | "#" <number> | "[" <dotnum> "]"

            <mailbox> ::= <local-part> "@" <domain>

            <local-part> ::= <dot-string> | <quoted-string>

            <name> ::= <a> <ldh-str> <let-dig>