First, let's explain what Abuse Emails are.
Abuse Emails are considered emails where the recipient clicks the "Spam" link often in emails sent to them. We call these high risk emails. If you email them, they might click the "Spam" link, therefore lowering your mailing reputation. Furthermore, these users contribute to causing your emails to land in the spam/bulk folders or, worse, not being delivered at all.
Now, should you send messages to Abuse Email Addresses? That's your decision. Maybe these people are really interested in what you have to say and they won't mark the mail as spam. It's your call, you know you customers better than we do and you know how you gathered these email addresses. Did you buy the list? If yes, maybe you shouldn't mail them. Are they an actual customer of your store? Then maybe you should email them. It's your decision.
How do we detect them? We have relationships in place that report this information to us. They are mostly gathered through Feedback loops or individual OPT-Out links found in people's emails.