[Mimedefang] Greylisting post-data (was Re: [PATCH] filter_data implementation)

- 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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