http://www.dirigodev.com/content/email-feedback-loops/
Tracking image loads and clicks would be a much more effective method of determining that an address is valid for both legitimate mass emails and spam.
How many people do you think load images versus click Report Spam on an ISP with a feedback loop? And which group do you think would be a better target for future messages?
There are laws regulating e-mail solicitations. People can be sued for SPAM, and incur criminal charges. Basically, if any mail provider notices that lots of its users complain about SPAM, they have legal standing to bring that person before a judge. Sending out a warning of possible legal repercussions is the first step.
Presumably, the spammer is contacted via e-mail with a strongly worded message, since it's very clear that they have the ability to interact via e-mail.
In theory, you as an individual, could run your own mail server, and if you received spam, you could threaten to sue or press charges. At some point before you actually do that though, you'd probably try to contact the person first. When cmwelsh uses the word "ping", that's just a euphemism for making contact, and not a specific technical term of any kind.
Among the consumer-grade ESPs, Mailchimp has a reputation for being extremely strict about anti-spam enforcement.