You can't outlaw spam since there are no worldwide laws. A lot of it comes from overseas now.

What you can do is implement some sort of whitelist. I saw a system a few years ago that would reply to incoming messages requiring a human response, automatically whitelisting the sender and allowing the original message through.

I considered implementing something like that on my personal mail account, but instead just stopped using it for now. I get about 300 spams a day on it, and I'm sure the disk is full on that machine. I should check it...and change my account name while I'm at it.