On Thu, 08 May 1997 13:12:42 -0400 "C. Harald Koch"
<[log in to unmask]> wrote:

> > We   have been informed by   Brad Knowles of   AOL  that they consider
> > section 7.5 of draft-ietf-drums-smtpupd-04.txt (still in draft status)
> > to be more important than RFC1123, which is in full standard status.
>
> This section talks about "use of the relay function through arbitrary
> sites". However, AOL's solution is also blocking *legitimate* use of the
> relay function. Internet firewalls and site-wide smart hosts are a couple of
> examples of legitimate uses.
>...

As the author of that text, there are three separate issues
here; confusion among them is unfortunate:

Q1: Is a site required to handle relay traffic that starts
from arbitrary sources and is destined for arbitrary sinks?

A: Nope.  Sites can decline to accept mail for
substantially any reason they feel like.  If the
sender or the intended recipient doesn't like it, he or she
can find a service with more attractive policies.  This
answer is unchanged from 1123 and, really, from 821.

Choosing to invoke this rule and refuse to accept mail is
essentially a business decision, even if it is motivated
by, e.g., moral outrage.

Q2: What is a receiving host which chooses to relay mail
expected to do about source routes?

A: RFC1123 and ...smtpudp-04 really differ very little
here. Both permit the receiver to either follow the source
route chain or to discard it and just use the target
address.  1123 is slightly weighted toward preferring the
former, smtpupd-04 is significantly weighted toward
preferring the latter, but neither behavior is prohibited
by either spec as long as it is done properly.

Q3: If you can find a host that is willing to accept your
relay traffic, do you need source routes to make that
happen?

A: Nope.  If I am sending mail to [log in to unmask], and using
x.y.z as a relay, I can open an SMTP connection to x.y.z
and then send it a message whose envelope contains
    RCPT TO:<[log in to unmask]>
Use of
    RCPT TO:<@x.y.z:[log in to unmask]>
is neither necessary nor desirable.  It was necessary for a
time in pre-DNS/ pre-MX days, but those are long gone.
Conversely, if I'm running host x.y.z, and I refuse to
accept your traffic for relaying, I'm going to do so
because I don't like you for some reason, and probably not
because you have chosen one of those forms over the other.

     john