Subject: RE: [Asrg] RMX proposals and Nash Equilibrium

From: "Eric D. Williams" <[email-masked]>
Date: Sat, 3 May 2003 21:15:30 -0400

All of these are valid points to argue, but without addressing a fundemental 
point (not described in most) RMX proposals from my understanding.  That is, 
DNS can also be used to validate an IP reverse map so that not only the domain 
is checked but also the IP.  In that case, IMHO, one could argue that an 
additional check for IP origination or relay of delivery would mitigate the 
concerns.

I could definitely be wrong but that always sticks out to me as a 
mis-understanding of that type of proposed solution/strategy.  I don't think 
the forwarder of mail has to be penalized for forwarding if they are properly 
registered in the forwarding path (open-relays are another matter in my 
opinion) and are no longer used in the historical context (helping a 
brother/sister system out).

On Saturday, May 03, 2003 5:51 PM, Daniel Feenberg [SMTP:[email-masked]] 
wrote:
>
>     An Economist's Take on RMX-style Proposals to Curtail SPAM
>
> In my understanding, the most cogent reason presented for why RMX
> protocols are undesirable is that forwarded mail retains the original
> envelope MAIL FROM, while coming from an arbitrary source.

The source is arbitrary only when an open-relay is involved.  Thus the 
forwarding path of a message should have determinacy.  I don't think eMail 
traverses random paths.  And if it does it shouldn't.  Maybe that is what needs 
to be fixed.

8<...>8
> Therefore I believe that the eventual equilibrium is that many domains may
> register allowed SMTP sources for their outgoing mail, and some will
> reject incoming mail which does not match one of the registered domains,
> but that essentially no sites will reject mail from non-participating
> domains and spammers will not use registered domains in MAIL FROM:
> addresses. Net improvement:  little or none.

I would reject mail from non-registered servers/domains if they were a spam 
source.  I don't think that messaging system managers ignore those types of 
situations and just allow all mail.  In fact I think we are moving toward a 
point where 'management' will demand the sysop to block all mail from, per se, 
unknown sources.

> Of course we are not at the final equilibrium yet, but the more relays are
> closed, the harder it is to maintain one. This could be called a "virtuous
> circle"  because once started it becomes stronger and stonger on its own
> accord.

I agree.

-e
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From: Daniel Feenberg <[email-masked]>
Date: Sat, 3 May 2003 23:19:27 -0400 (EDT)

> brother/sister system out).

Perhaps I wasn't clear. If [email-masked] adds the line:

     joe: [email-masked]

to the system aliases file, then mail arriving from source.com will be
forwarded to example.net. But example.com will not be on the list of
authorized originators of source.com mail, and if example.net rejects
for that reason they may be rejecting perfectly legitimate mail. 

It really has nothing to do with relays, open or otherwise.

I mentioned the Sendmail REDIRECT feature as a possible ameliorative
feature for this problem. Sendmail could be configured to reject the mail
for joe at example.com with a 551 error and give the forwarding address in
the error message text, allowing the original sender to try again at the
new address. I don't know of any MTA or MUA that would automate that
process, nor does a half hour with Google turn up any mention of REDIRECT
used in this context. But it is mentioned several times in RFC 1123,
specifically in Section 3.4 as return code 551. I am not suggesting that
this is a real solution to the problem, but it is an example of what sites
might turn to if RMX proposals were widely adopted.