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[spf-discuss] Re: Better approach to the forwarder problem

2007-01-15 14:34:34
Dick St.Peters wrote:
 
Lessee ... STD 10 (better known as RFC 821) said:
[...]

Among other things it has this:

 [in 3.6 relaying]
      Conceptually the elements of the forward-path are moved to the
      reverse-path as the message is relayed from one server-SMTP to
      another.  The reverse-path is a reverse source route, (i.e., a

 [in 4.1.1 MAIL]
      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).  In some types of error

 [in 3.1 MAIL]
      The <reverse-path> can contain more than just a mailbox.  The
      <reverse-path> is a reverse source routing list of hosts and
      source mailbox.  The first host in the <reverse-path> should be
      the host sending this command.

 [in 3.6 RELAYING]
      If when the message arrives at an SMTP the first element of the
      forward-path is not the identifier of that SMTP the element is not
      deleted from the forward-path and is used to determine the next
      SMTP to send the message to.  In any case, the SMTP adds its own
      identifier to the reverse-path.

That 1123 somehow did away with reverse paths back through forwarding
hosts is pure myth.

 [in 1123 5.2.6]
      A Sender-SMTP SHOULD NOT send a RCPT TO: command containing an
      explicit source route using the "@...:" address form.  Thus,
      the relay function defined in section  3.6 of RFC-821 should
      not be used.

      DISCUSSION:
           The intent is to discourage all source routing and to
           abolish explicit source routing for mail delivery within
           the Internet environment.  Source-routing is unnecessary;
[...]
      DISCUSSION:
           For example, suppose a host that does not implement the
           relay function receives a message with the SMTP command:
           "RCPT TO:<@ALPHA,@BETA:joe(_at_)GAMMA>", where ALPHA, BETA, and
           GAMMA represent domain names.  Rather than immediately
           refusing the message with a 550 error reply as suggested
           on page 20 of RFC-821, the host should try to forward the
           message to GAMMA directly, using: "RCPT TO:<joe(_at_)GAMMA>".
           Since this host does not support relaying, it is not
           required to update the reverse path.

RFC 1123 changed the original RFC 821 strategy any explicitly says so.

Frank


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