In our case, we're a small business, and we don't do email marketing. So I'd say that anything of ours that gets dropped by Outlook isn't trash. The only non-hand-typed email we send are transactional - actually transactional as in "here's your invoice" or "here's you're tracking number".

You know, you could achieve 100% spam filtering by just deleting every email. You wouldn't see any spam at all!