If you are looking to prevent a contact from being added to a Sequence, you can unsubscribe them from the Sales Email | One to One subscription. However this will prevent the contact from receiving all One to One emails, not just Sequences.
If you are looking to prevent a contact from being added to a Sequence, you can unsubscribe them from the Sales Email | One to One subscription. However this will prevent the contact from receiving all One to One emails, not just Sequences.