Daz: Spam filters work by using a learning algorithm that recognizes sequences of words that most likely constitute spam. Usually it doesn't matter who the mail is from. Since the filters don't delete the mail but move it into a spam folder you can just look in there if it has caught any false positives.
I never use Outlook anymore so I don't know any that work with it. Mozilla Thunderbird does a great job filtering out spam. I use it at work. I check through my spam folder on occassion to make sure it didn't filter out any important emails and it's only done that a few times in the last year or 2 I've been using it.