Subject: Re: [Fwd: [Asrg] Re: Documents for LMAP BOF]

From: "Alan DeKok" <[email-masked]>
Date: Mon, 09 Feb 2004 10:38:19 -0500

Yakov Shafranovich <[email-masked]> wrote:
> If the entire purpose of these proposals is to make sure that the sender 
> is who he claims to be according to DNS information,

  I would say "has permission to claim association with a domain"

>  than what we could 
> do is create an ESMTP extension to pass sender's information to the 
> server MTA which will be verified via DNS. Since we need to change MTA 
> software to support sender rewriting schemes, we might as well add a new 
> extension instead, to pass that information explicitly.

  Sounds fine to me.  Can we have a show of hands from people in the
IETF who are *not* opposed to modifying SMTP?

> Of course this is just devil's advocate speaking :)

  Yes, and there are standard arguments against it:

 - it will take too long to deploy
 - it won't stop spam.

  My responses are:

 - it will take less time to deploy than waiting forever for a perfect
   solution
 - it's not intended to stop spam.  It's intended to allow the
   recipient to better deal with the spam he does get.

  99.99% of the spam I get is forged.  Call me naive, but this says to
me that spammers believe that forgery is an important part of the
spamming process.

  This addition would also get rid of the forged viruses & worms.  If
nothing else, it would make it plainly obvious who's stupid enough to
run a system which gets viruses.  Right now, I don't get viruses, but
I get tons of spam from software by antivirus companies, claiming to
have found a virus in a message I sent.  The fact that the viruses are
forged, and that their "notifications" are spam, is something the
virus companies apparently don't get.

  Alan DeKok.

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From: Yakov Shafranovich <[email-masked]>
Date: Mon, 09 Feb 2004 14:16:53 -0500

> IETF who are *not* opposed to modifying SMTP?

I am not talking about modifying SMTP itself, rather adding an optional 
ESMTP extension to it. Servers using this extension would be 
whitelisted, giving people incentive to use it. Servers, that do not 
will be treated like they are today. The underlying SMTP protocol will 
not be modified in any way.

In SMTP AUTH RFC there is an AUTH parameter for the MAIL FROM command 
which indicates the sender. If you use some similar mechanism to pass 
sender information, you do not have to mess around with changing the 
semantics of the envelope sender that are defined in RFC 2821.

Of course, that would assume that you trust the MTA which brings us back 
to two separate problems:
1. We are trying to authenticate the incoming MTA.
2. We are trying to authenticate the relationsh between the sender's 
domain and the incoming MTA.

DRIP addresses #1, while the other LMAP proposals address #2. What I see 
as a problem is that sender's identity is not being explicitly given, 
rather it is implied from #2. I would be much happier if the incoming 
MTA would pass me the sender's identity and the question of 
authentication of MTAs would be separate.

For example, with DRIP you can tie MTAs to domains and then to a 
reputation service for IPs/domains of incoming MTAs. Then you would have 
a separate mechanism for passing the sender's identity. This would 
protect you from having trusted MTAs relay spam from hijacked computers 
  since the two identities will remain separate.

> me that spammers believe that forgery is an important part of the

Well the question is, imagine is the email system had identity. Would it 
have made a difference?

Yakov
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Yakov Shafranovich / asrg <at> shaftek.org
SolidMatrix Technologies, Inc. / research <at> solidmatrix.com
"Be liberal in what you accept, and conservative in what you send" (Jon 
Postel)
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