According to CAN-SPAM, you must include way to opt out from your email if you are sending commercials emails. Whether it is cold emails (unsolicited emails to recipients you have had no interaction with in the past) or marketing newsletter, you have to offer a way to unsubscribe.
At the moment, we don't provide a built-in solution to add unsubscribe links into your emails sent with Mailmeteor.
Solution: you can add a link pointing to a Google Forms to let people opt-out from future communication. Then, you can remove these people from your contacts lists.