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Re: What is GreyListing

Christian Hammers <ch@lathspell.de> writes:

> Hello
> On 2004-07-20 Russell Coker wrote:
>> (host mail3av.westend.com[] said: 450 <ch@lathspell.de>:
>> Recipient address rejected: Greylisted for 300 seconds... (in reply to
>> > RCPT TO command)) ch@lathspell.de
>> Christian's mail server is broken.
> Err, no. It's not a bug it's a feature :-) Called "greylisting".
> In opposide to normal black- and white-listing here postfix has an
> additional policy daemon that checks if the tripel "sending ip, from,
> to" is already in the database and if not, reply with a 450 aka
> "temporary(!) failure" code and take note of it.  If it's a real
> mailserver and not a trojan-winXP-desktop then it will try it again in a
> couple of minutes. If it does the above tripel will be whitelisted for
> the next days/month/whatever.

This sounds suspiciously like (dangerously stupid) challenge-response
systems.  How does this differ?

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