In rare instances, contacts may abuse your service or send offensive messages. You can block these contacts by navigating to the "contacts" tab, highlighting the contact, and clicking the "Block" icon. All incoming messages from blocked contacts will be archived.
Furthermore, flows will not send to blocked contacts, which is useful for restricting sending to contacts who've opted-out from messages.
You may unblock a contact at any time by clicking on the "Blocked" sub-category underneath the "Contacts" header, clicking the box to the left of their name, and clicking the "Unblock" button.