[exim] DNS based host name Whitelists

Here's an idea that I'm thinking about in my fight against spam. DNS
lookup of hostnames that NEVER send spam. That way you can make sure
that some good email is never misclassified as spam. And you can reduce
the load on Spam Assassin or other expensive filtering by bypassing spam
testing.

That are a lot of servers out there than never send a single spam. So -
why not track them and build a DNS whitelist server to distribute the lists?

Stop me if it's been done already.

Then - I'm also working on the idea of a second white list of hosts that
should never b accidentally blacklisted. The idea here is to prevent
hosts that send some spam, yahoo.com, earthlink.net, from ending up in a
blacklist. This will make it so that the blacklists have less falso
positives.

So - who likes this idea?