For me, spam is easy. About 99% of it is rejected by using a regex methodology created by a gent in japan that he named "S25R". [1]

[1] - http://www.gabacho-net.jp/en/anti-spam/anti-spam-system.html

I've been using that for about 15 years. Works great. I even implemented it in a medium sized company. The only issues it caused were former employees that were running mail servers on their cable modem and stealing customers for their small businesses.