Opt-outs have two halves: the plumbing (what happens when someone replies STOP) and the wording (telling people they can). The plumbing is automatic; the wording is yours, and TextBay helps with both.
The plumbing: STOP replies #
When someone replies STOP (or UNSUBSCRIBE, CANCEL and similar) to a US or Canadian number, two blocks happen without you doing anything:
- Twilio blocks them on its side. Any later send to that person fails with error 21610 until they text START.
- TextBay blocks them on yours. The inbox detects the STOP reply and puts the number on your local block list, so future runs skip those people outright instead of burning sends on 21610 failures. The same happens when a run hits 21610 directly.
The block list lives on the Contacts page under Blocked numbers; the Reason column says who opted out versus who you blocked by hand, and you can unblock someone who asks back in.
The wording: your opt-out line #
Twilio adds no opt-out wording to your texts. For marketing to US and Canadian numbers, carriers expect the first message (and an occasional reminder) to say how to stop. The composer’s Add an opt-out line button appends “Reply STOP to opt out.” once; purely transactional texts can usually go without it, and when in doubt, include it.
Two channels play by different rules. WhatsApp has no STOP keyword (people block the sender instead), so the button hides on that channel. Sender names cannot receive replies at all, so STOP is impossible: include a different opt-out route and honour it by hand. See Sender names.