In order to use the SMS add-on to send SMS to contacts, the contact has to be set as a Marketing Contact, they need to have the +1 country code (in the US) in their phone number, and they need to have their Subscription Status set to Subscribe for the Communication Subscription Type of Marketing SMS. I have all of this set up as a part of a workflow. My question is, when a contact opts out of receiving texts manually by texting STOP, does that set the Subscription Status of their contact record to Unsubscribe? If yes, does enrolling them through this same workflow override their preference and re-subscribe them? If not, is there a Contact Property that reflects the fact that they have opted out and can I build an Active List around that Contact Property?