What is GreyListing (was: Re: Christian Hammers...)
On 2004-07-20 Russell Coker wrote:
> (host mail3av.westend.com[188.8.131.52] said: 450 <email@example.com>:
> Recipient address rejected: Greylisted for 300 seconds... (in reply to > RCPT TO command)) firstname.lastname@example.org
> 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 mechnism has reduced our Spam amount drastically even on a mail account that had already SpamAssassin active.
(It's installed at the ISP where I work and currently in beta testing.
The nearby university already uses it with great effort.