RE: blowback, was A new SMTP "3821" [Re: FTC stuff...........]

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Dean Anderson
> Sent: Sunday, January 09, 2005 7:39 PM
> To: [email protected]
> Cc: [email protected]
> Subject: RE: blowback, was A new SMTP "3821" [Re: FTC
> stuff...........]
>
>
>
> On Mon, 3 Jan 2005 [email protected] wrote:
>
> >
> > Dean Anderson wrote:
> > > The blowback issue is different from this.  Blowback
> happens whenever
> > > anyone _rejects_ emails based on SPF.
> >
> > Fair enough
> >
> > > A bounce is generated from the relay to the forged sender.
> >
> > Is it?  If the receiving MTA issues an SMTP reject command,
> it does not
> > assume any responsibility for the delivery of the mail.  It will
> > therefore not generate a spurious bounce message.
>
> This isn't how most current SMTP servers behave.
> (Sendmail/Qmail/Postfix/Exchange, anyway)  If the receiving
> MTA rejects
> mail, the sending MTA generates a bounce to the sender.  The
> sender of
> course, can be forged.

Agreed, but near sighted.  If the sending MTA had done some sort of validation to ensure the message
was not forged when it accepted it, then we wouldn't have a blowback problem.  You cannot blame
subsequent MTA's in the path for detecting and rejecting bad email when its something the first hop
MTA could (and should) have done in the first place!

His point I think is that if the virus is trying to send directly to the MTA it would get rejected
with no bounce back (because the virus wouldn't process a bounce).

If an MTA.1 accepted a virus message, and tried relaying it to MTA.2, when MTA.2 rejects it as
forged, and MTA.1 processes a bounce, well, NO SYMPATHY FOR MTA.1, it should have taken steps to
prevent the virus/forgery etc from being accepted by itself in the FIRST PLACE.

>
> > If the sending MTA generates a bounce message, then it's
> likely not a
> > virus or other malware likely to forge a sender address.
>
> ???
>
> This too is wrong. Many viruses send "forged" bounces
> containing a virus.

The statement was that virus infected machines don't usually process bounces if an MTA rejects its
transmission attempt.  And the statement *is* correct.

> One cannot assume that because you opened a bounce, the
> message will not
> contain a virus.  Further, a genuine bounce with an
> undelivered message
> may contain a virus in the undelivered message.

True, but what is your point?  The question at hand was "If the MTA rejects a message, does this
cause a blowback problem":
Case 1: Message is arriving from the virus itself:
-no blowback, viruses will usually ignore the rejection

Case 2: Message is arriving from an MTA that accepted the message from a virus:
-no sympathy for the bounce, the MTA should have rejected the virus message in the first place.
Is there a real issue with blowback?  NO:  There are plenty of ways of dealing with blowback until
all the MTA's are upgraded to provide some sort of MTA authentication to deal with forgery and
reject it at the first hop.  (Yes, even silently dropping the bounces, something which large ISP's
often do already ANYWAY).

Terry Fielder

>
>
> > Matthew.van.Eerde (at) hbinc.com                 805.964.4554 x902
> > Hispanic Business Inc./HireDiversity.com         Software Engineer
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> >
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> >
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