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Re: Strong Opposition due to spam backscatter. Re: Last Call: draft-ietf-sieve-refuse-reject-07 and -08 (Sieve Email Filtering: Reject and Extended Reject Extensions) to Proposed Standard

2008-09-11 12:25:28

A little additional perspective on this from someone who has
(deliberately) not been active in the SIEVE effort.   Cyrus has
alluded to some of this, but the real constraint is with SMTP,
not  SIEVE, and should be addressed in the SMTP context.

The issue of NDN blowback has come up repeatedly in discussions
of SMTP.  The bottom-line answer, despite complaints from
zealous anti-blowback advocates and clever alternate readings of
the spec, is that the SMTP model simply doesn't work without the
possibility of non-delivery messages.  While there are other
issues, the most important and obvious of them is that SMTP
permits and encourages multiple-recipient messages and has no
in-protocol mechanism for returning per-recipient replies.  

In theory, that problem could be overcome with an SMTP extension
for per-recipient replies.  There is a long-expired I-D that
discussed doing just that, but it never got an traction (and may
or may not have been the best way to do it).  However, while
per-recipient responses have other advantages, there is no
reason to assume that spammers would voluntarily make their
lives more difficult by invoking such an extension.

Conversely, the blowback problem could be solved in principle by
authenticating message senders (probably beyond their
authorization to send mail, which is more or less the problem to
which DKIM and SPF are addressed).  But there is again a
deployment problem unless one assumes that legitimate deployed
SMTP implementations can be changed in only a short period of
time.  See
and the surrounding context for further discussion on that issue.

The bottom line is that a debate about prohibiting SIEVE from
returning NDNs is meaningless without changes to SMTP.  We don't
have any proposals on the table for such SMTP changes and don't
know how to get from "here" to "there" with any of the proposals
that have been made.    I guess that makes this I-D a more
tempting target, but it still does not make it relevant.

If the SIEVE WG somehow decided that it liked one of the
proposals for suppressing the possibility of NDNs, we would then
be having a discussion about whether or not that WG is permitted
to write a spec that requires violations of SMTP.  Fortunately,
they did not present us with that choice.


--On Thursday, 11 September, 2008 10:38 -0400 Cyrus Daboo
<cyrus(_at_)daboo(_dot_)name> wrote:

Hi Matthew,

--On September 10, 2008 3:13:33 PM -0700 Matthew Elvey
<matthew(_at_)elvey(_dot_)com>  wrote:

Lisa D reported being told: "There is strong WG consensus
behind [-07]". Lisa D specifically claimed the WG chairs
indicated there was.  CHAIRS: Can you each please confirm
that you stated that there is strong WG consensus behind

Yes, I can confirm that and firmly believe that the overall
consensus of  the WG is to publish the -07 draft. I don't
believe there is a need to  re-poll the WG on this, but if the

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