RE: [Asrg] New proposal for spam blocking: Greylisting

[Evan Harris <eharris@puremagic.com>]

It should be noted that the 30% is actually quite a low estimate of the
effectiveness, which was based on numbers derived from a slightly similar
implementation.  But the newer implementation has significant advancements
that make a marked increase in the effectiveness, as many others are coming
to realize as they start implementing it.

Here's a key quote from a user on the greylisting-users list hosted at
http://lists.puremagic.com/

> RBLs are weak when new ip addresses are used to spam. Greylists are weak
> when the same ip address is used for repeated spam. Combined they can work
> better than either alone since each attacks the others weakness.
> - Martin Dempsey

Evan


On Sun, 22 Jun 2003, Vernon Schryver wrote:

> > From: "Elric Pedder" <elric@novitraq.com>
>
> > ...
> > Regardless, I'm not an advocate of greylisting.  I agree with
> > the points you and others have made and the most significant is
> > that it has a relatively short life span.  However it is one of
> > the more interesting solutions to appear recently.
>
> I agree with the last sentence, but not all of the rest.  Others have
> reported that similar tactics are around 30% effective.  The high
> effectiveness reported here might be because, as was said, the high
> rate included dictionary attacks.  You'd expect dictionary attack spam
> to be particularly likely to be "hit-and-run."
>
> My random guess is that should it become popular, its effectiveness will
> drop from 30% to 10-20%, because it will ever become universal and many
> spammers blocked by it will choose to send to more addresses than go to
> the substantial trouble to send to the same targets through the same open
> proxies.  If I'm right, 10-20% is nothing to sneeze at, and is as good as
> or better than the realistic prospects of several other, purely theoretical
> spam defenses whose advocates promise us more.
>
> Note that greylisting can be seen as a variety of quarantine mechanism.
>
>
> Vernon Schryver    vjs@rhyolite.com
>
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>




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