We have a policy designed to scare off career spammers (not "my client spammed without my knowledge" or "I had a password compromise and my account was used to send spam without my consent"). The policy is to bill $1 per spam email sent, and terminate the account. The latest, we even suspected them and warned them in advance. They still did it. That makes them our new scarecrow. May they fly high and review loudly.
Legal content allowed, don't be a dick.