Re: [NTISP] Spam Filtering

David Payer ( (no email) )
Sun, 7 Mar 1999 07:42:41 -0600

>As for reverse DNS, the only thing I have seen where it is even remotely
>useful is for companies who use a reverse lookup in conjunction with a
>trace to determine whether or not you are eligible to download a strong
>encryption product. And even then, all one needs is a shell account in the
>U.S. to get around that.

You are correct that those who know how to can easily bypass the issue of
screening against reverse lookups. But my point is this: the MAJORITY of
spam comes from those marketers who want to find a quick way to send out
multiple thousand emails. I did a review of logs for rejected addresses and
tested many by telnetting back to port 25. Over 95% of those tested did not
respond on that port. For the more dedicated spammers, the Real Time
Blackhole List filters will be helpful.

My problem when I do filtering is that some corps use firewalls and don't do
inverse addressing and then their workers send mail back to their home
account on our service and we reject it due to inverse addressing filters. I
find that there are administrators who will reject you out of hand regarding
setting up their network with this one precaution.

I again assert, if we don't make efforts to stop spam ourselves, we will
have governmental assistance in doing that. This will come with an
accompanying tax to pay for administrating it. Once that mechanism is in
place, the influence will grow (remember: income tax was originally never to
exceed 3%).

OK </republican-jargon>

David Payer

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