[Greylist-users] Greylisting with automatic IP address based whitelist

Harald Schmitz harry at fh-aachen.de
Thu Jun 17 07:52:47 PDT 2004

Akihiro KAYAMA wrote:
> Hi all.
> I have a fundamental question About Greylisting. This is not explained
> in Greylisting whitepaper. I want to know any URLs if already
> discussed.
> My question is the reason why Greylisting does not use automatic IP
> address based whitelist.
> When a particular site has been successfully probed by triplet, it is
> reasonable to consider the site to be driven by legitimate MTA. So if
> the site deliver subsequent mails with different sender/recipient, as
> long as IP address is the same, next probe should be the same result.
> In this point, Greylisting with IP address based whitelist will
> accomplish the same result, and significantly reduce delayed mails.
> ISP's dynamic IP addresses is not a problem because there is few
> servers on such addresses, clash with open proxy host is still rare.
> Anyway, I have modified my greylisting script to do so and happily
> enjoy greylisting power without special care about Ezmlm. I can't see
> any evidence that same IP address host occasionally runs both
> legitimate MTA and open proxy.
> Any comments will be appreciated.
> Thanks.
> -- kayama
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Hi Kayama, 

the reason why we don't use these feature is the fact that:

greylisting blocks often 100% Spam / Viruses from a IP, but
NOT ever.

Sometime there are random delivery retries, that make this possible. 

My practical knowledge shows a blocking average of  95 %, so
you will whitelist 5% of the spamming IP's.


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