OT: Grey-listing?

[Matt Kettler]

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Kevin Miller wrote:
> James Gray wrote:
>
>>For those who are interested, in the first 24 hours of operation our
>>spam is down by almost 40% and server load down by about the same.
>>Those numbers are
>>%-age of what was happening prior to implementing milter-greylist.
>
>
>
> Cool.  Sorry for being dense, but in 25 words or less can someone explain
> greylisting?  Blacklist and whitelist are obvious, but I'm not quite sure
> what happens with a greylist.

When mail arrives from a new server, generate a 4xx series temp fail. Continue
to 4xx mail from said server until a greylist period X has expired. If they come
back and retry after the greylist period, accept the mail.

The basic gist is to verify that a server is actually a real mailserver that
properly retries messages and not a "one shot spamrun" tool.

Exact implementations vary greatly and greylist periods vary from 1 minute to a
few hours depending on the person running the greylist. Most greylists will also
auto-whitelist mail from a server for a few days once it passes this test.

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