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Clifton Royston wrote:

> On Thu, May 19, 2005 at 10:49:54PM +0200, Lazar Obradovic wrote:
>
>> Hello all,
>>
>> Are there any reasons not to introduce greylisting (GLing)
>> functionality in amavisd-new?
>
>
> Yes, IMHO, it belongs in the "front-end" MTA.
>

Yep. It doesn't make sense to doit anywhere else. FWIW using postfix
with address verification will catch a fair amount of this traffic as
well. For the same reasons. However postfix only operates on the
sender address itself. And doesn't consider the sending IP address.

For example at work I have address verification enabled on postfix.
For every 100k emails we catch about 4k spam emails at
amavisd/spamassassin. Which looks really low, until you include the
600 rejects a minute just from address verification (That 600/min
doesn't include the 4xx replies for verification in progress BTW).

I'm not sure that greylisting as described would add a lot to postfix
address verification though. But it would be nice to try even just as
an experiment to see how many of the 4% of spam was cut down by
greylisting...

One thing I do notice though is the assertion that most spammers don't
retry the emails. It's been my experience with address verification
that most spammers who use invalid sender addresses don't even
consider a 5xx. They just seem to keep retrying for ages.

> amavisd is designed to sit "behind" the MTA and cooperate with it;
> graylisting needs to happen at the edge.
>
> You can use amavisd and graylisting in combination, with amavisd
> sitting behind and catching the stuff that gets through
> graylisting.
>
> -- Clifton
>

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