[spookthesunset]

> "spam can be filtered objectively"

"Objective filters" (by which I assume you mean "rule based") can easily be worked around by the people trying to get through the filter. All you gotta do is figure out the rule and bam, you are back in again.

Sure it might work for your tiny little family domain name with your tiny 10 mailbox email server. No spammer gives a crap about you. But when you are on the scale of gmail, you will have a lot of people whose entire purpose in life is getting through your spam filters. "Objective filters" turn into a continual game of whack-a-mole. Put in a rule, wait half a day until somebody works around that rule, put in another rule.... repeat ad nauseam.

"Objective Filters" don't scale at all. They might filter out the riff-raff script kiddies but anybody whose livelihood is based on getting past your "objective filters" will easily overcome them.