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Re: TMDA backscatter

2007-10-09 14:11:15
Returned message content in DSNs is often essential information for
debugging of mail system problems.   Blindly insisting that DSNs should
not return subject message content is shortsighted.  We have already
crippled the mail system too much as the result of naive and
shortsighted spam countermeasures.

Keith

Yes, DSNs that include content are a problem.  Dropping NDN or DSN
that indicate a failure of some sort also makes email less reliable. 
Email has become far less reliable as a result.  The TPA-SSP scheme
for DKIM allows a return path to authorize the DKIM signature only to
encourage the issue of DSNs.  Again, those DSNs should still exclude
original message content.

A safer approach would be to format all DSNs per RFC3464 and remove
original message content.

I'd hope that a majority of receivers already does this, that's state
of the art for some years now.  Or rather "truncate" is state of the
art, not complete removal of the body.

It would be rather tempting to make this mode of DSN operation a
requirement.  At any point of time, we see some 20 million different
MTAs which do not remove message content are currently being
exploited.   Perhaps we should add a new list that indicates which
MTAs do not remove content on DSNs?  We could then let our customers
decide whether they want traffic from these MTAs as well.  Not all
that different from open-proxies and aimed at restoring DSN integrity.

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