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Re: [Asrg] Re: bounces, and anit-spam principles

2007-01-23 06:33:25
On 1/23/07, Peter J. Holzer <hjp-asrg(_at_)hjp(_dot_)at> wrote:

Temporarily block emails from this user and generate a bounce message

...

Sounds like a nice scheme to me. Has anybody ever tried that?

I don't know if anyone has tried it, but we discussed a proposal at
Apache James some years ago that proposed using a 4xx response to
allow recipient MTA's to spend time evaluating (or hand off evaluation
of) an mta's or sender's identity (possibly scoring it) before
accepting mail from them rather than perform expensive checks in real
time. I briefly mentioned it on this list in 2003[1] I believe that
this approach is also consistent with rfc2505 para 1.6[2].
The sending MTA would either retry after an agreed delay, or when
called with an enhanced ETRN, enhanced to specify allowable MTA's,
sender(s) and/or recipient(s) or listed message id's (not the ones in
the body, this would have to be a key agreed between MTA's).
In the event that the recipient decides not to allow it would return
another 4xx with an appropriate reason that might be resolved, or a
5xx with a reason which could not be resolved.
The main objection was that some felt the quantity of delayed mail and
the reconciliation of it against the allowable patterns would impose a
significant unwanted overhead on MTA's. We didn't do any analysis to
confirm or refute this.
A less crucial objection is that badly behaved sending MTA's wouldn't
abide by the rules and even though connections could be broken and 4xx
& 5xx re-issued it might not be possible to realise the perceived
benefits when challenged by a load of badly behaved spambots.


d.
[1] http://www1.ietf.org/mail-archive/web/asrg/current/msg06019.html
[2] http://www.ietf.org/rfc/rfc2505.txt

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