The amount of spam is growing day by day, with no signs of an abatement in volume. Filtering means you, your ISP, and your system have to work harder to filter out junkmail. You Still Get Spam. In order for this to work, you have to receive the spam in the first place. It Doesn't Work.
Most spam is forged in some fashion, making it impossible to determine the origin.
No matter what filtering mechanism is built, spammers will find a way around it. Not worth getting worked up over. What they don't tell you is that in order to deliver that message to you, other people paid for it. If spam manages to become legitimized, then 500 messages a day will be small potatoes. You can get into a lot of trouble for attacking another computer or network.