[Mimedefang] Greylisting post-data (was Re: [PATCH] filter_data implementation)
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kd6lvw at yahoo.com
Wed May 27 18:55:25 EDT 2009
--- On Wed, 5/27/09, David F. Skoll <dfs at roaringpenguin.com> wrote:
> Martin Blapp wrote:
> > Ask David, AFAIK he's using such a post DATA graylisting
> > implementation, but at filter_begin() instead of filter_data().
>
> Yes, we filter post-DATA for two reasons:
>
> 1) To make greylisting work with marginal SMTP servers that don't handle
> 4xx responses to RCPT properly.
I can accept that - although I've never knowingly observed it.
> 2) We greylist on: HASHFUNC(sender, recipient, sending_ip, subject)
> because some spammers got around greylisting by sticking to the same
> IP address, but mutating the subject header. Because we include the
> subject line in our greylisting mix, we couldn't greylist in filter_data
> even if it were available.
However, if subject were not part of your mix, then greylisting (with a "421" as that's really the only temp-error code that should occur in response to DATA) would work.
I was just looking for a potential use. Looks like there is one.
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