Hello Kristen,
Others have provided great advice. CAN-SPAM provides provisioning for a "transactional email" that is relating to goods or services that someone has purchased and does not include marketing content. Using the operational email option in Marketo means that you will be sending to leads who are unsubscribed. Since there are many reasons that someone might be using your product but have chosen to unsubscribe from your marketing emails, it makes perfect sense that this information should still go to people who are unsubscribed. You'll want to be careful to make sure the email is fairly matter-of-fact and doesn't come off as promotional, but other than that, this is exactly the reason we created the operational email feature in the first place.