Whenever I unsubscribe from yet another Mailchimp list I've been added to, I typically select "the emails are spam and should be reported". What does this actually do on the other end?
Your email address is moved to the Abuse Complaints Area and the sender of the bulk emails is notified. If complaints start accumulating from several recipients, MailChimp launches an investigation against the alleged spammer.
[What happens if] I got an abuse alert in my account
At first, you should take an abuse alert as a "heads up" that people are complaining about your campaigns. If you get more complaints than a small handful, you should be concerned and we highly recommended to re-evaluate your email marketing process to prevent further complaints.
Once abuse complaints exceed our threshold you will receive a warning notice. If the complaint rate is far beyond that threshold, a suspension notice will arrive in your inbox from our abuse team. They will ask about your list collection process and ask for other details about the health and life of your list. We'll need that information because by then ISPs and anti-spam organizations are threatening to blacklist us unless we explain why your list generated so many complaints. A full investigation will proceed once we have the requested information from you.