Maybe five, total, but all five were like drop-dead important.

We use GFI Mail Essentials on an Exchange box.  Apparently, he'd never had a false-positive when we used spamassassin and postfix.  I know this is not true, but myopia, etc.

So the most important issue right now is: where do we find a perfect spam filter?

We're investigating a combination of a barracuda box and cloudmark.  Cloudmark makes a host-based piece, I believe.  They get good ratings for their server product...fewest false positives out there.

So, in short: maybe cloudmark.  Maybe not.  I really don't think there's a good way around it from the host side.  On the server side, I need graylisting and whitelists and absolute perfection which I hear is about as possible as me winning this lottery I haven't entered.
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"You bring the weasel, I'll bring the whiskey." - kellnerin