Reverse DNS lookup - how to stop spam with Exchange 2003


I have read multiple questions on EE regarding this, none of them answer my question - how do I use reverse DNS lookup to block spam emails? I realise that the 'use reverse DNS lookup on incoming messages' checkbox in SMTP properties just adds the resolved name to the header, what I am looking for is a way to block emails on the basis of reverse DNS lookups, much like AOL do. Is it an Exchange setting?
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The perform reverse DNS lookup option that is built in to Exchange is close to useless. It doesn't actually block anything, just carries out the test.
You will need to use a third party tool to actually block the application, or a RBL.
Personally, I am having some success with Vamsoft ORF. It is priced per server and sits in front of the Exchange server.

SPF is also useless on its own. The deployment isn't wide enough to actually make use of it, so the most you can do is use it along side something else to score the message as being spam (or not).

IMF does quite a good job with some sites. You can enable it without actually getting the product to do anything, just scan. Then use perfmon to monitor what it is doing.

I believe your refering to something called SPF (Sender Policy Framework,) in whch the recieving server does a reverse DNS lookup to verify the identity of the sending server.  I do not believe this is part of exchange.

I would not say this is standard practice just yet so you could lose e-mails from people sending you mail whose servers do not yet have the reverse DNS record added yet.
Here is some more information about SPF


5t34lth_G33kAuthor Commented:
thanks to all for their input - its a shame take-up on SPF isn't widespread, as that could potentially solve all our problems. We cannot risk losing 'real' emails, however, so this will have to wait.

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