(skip to 2:45)
The _only_ thing that works (yes! actually works!) is if you forcefully whip out your credit card immediately upon receiving a spam and order one (1) of the items they are selling.
This seems to appease them, and they respectfully stop sending more E-mails.
Also, after sampling several hundreds of products, you might notice that your penis has become the second largest gravitational attractor in the solar system.
Good luck, and keep those planets orbiting!