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

David F. Skoll dfs at roaringpenguin.com
Wed May 27 17:31:57 EDT 2009

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.

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.



PS: To make our greylisting tolerable, we mark a host that successfully
makes it past greylisting as not-to-be-greylisted for 40 days.

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