RE: [NTISP] Spam Filtering

David V. Brenner ( (no email) )
Sat, 6 Mar 1999 21:30:05 -0800

> spam...not the absence of reverse lookup on an IP. If only 10% of the
> clueless admins would buckle down their mail servers and not allow
> mail relay I bet it would cut 50% of the SPAM. Needless to say we had
> to remove blocking mail servers that had open relay...too much mail
> was being rejected.

We relay only for our own address blocks. Anything else is considered on a
case-by-case basis. This decision was made very early in my learning days,
after I'd spent half a day trying to clean out the 200,000 queued messages
that some spammer had crashed my server with.

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 whois
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.

Lastly, where delegation of assigned numbers is concerned, any decent
upstream provider will allow you to use shadowing or aliasing to control
what's returned by reverse queries. This can even be done on a 4-host

David V. Brenner -
International Services Network Corporation

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