STOP keyword: definition and how it works
Published and updated
STOP is the conventional reply a recipient sends to opt out of a sender's text messages, which the sender must recognise and honour by ending the messages and confirming once.
How it works
Every messaging programme needs a way out, and the industry settled on a reply keyword. STOP is the canonical one; the CTIA principles and most carrier programmes also expect END, CANCEL, UNSUBSCRIBE and QUIT to work, and HELP to return information about the sender. On carrier routes that use short codes, the carrier itself may intercept STOP and block the sender before the message reaches you. On long codes and phone numbers the reply comes to you and your software has to act on it.
Acting on it means three things. Record the opt-out against the number immediately. Send one confirmation, and only one, saying the person has been unsubscribed and will receive nothing further; that message is expected and is not treated as marketing. Then send nothing else to that number until the person opts back in, which the keyword START or a fresh consent usually handles.
Match generously. People write stop with a full stop, in lower case, as part of a sentence, or as please stop texting me. United States regulation says consent may be revoked in any reasonable manner, so a rigid exact match is a liability. Treat any message that plainly asks you to stop as an opt-out and let a human review the ambiguous ones.
Keep the opt-out list separate from your marketing data so a re-import cannot resurrect a number.
- The CTIA Messaging Principles and Best Practices expect senders to honour opt-out requests from recipients. api.ctia.org, checked on September 4, 2026
How this applies with textbee
Replies to your textbee number arrive as MESSAGE_RECEIVED webhooks or through GET /gateway/messages. Match STOP and its variants there, store the opt-out, send the single confirmation with POST /gateway/send-sms, and check the list before every campaign send.
Related terms
- Opt-in: Opt-in is the recipient's recorded agreement to receive text messages from you, collected before the first message and kept as proof, with a higher written standard for marketing.
- TCPA: The TCPA (Telephone Consumer Protection Act) is the United States law, implemented by the FCC in 47 CFR 64.1200, that requires prior express consent before automated calls or texts and written consent before marketing ones.
- Two-way SMS: Two-way SMS is messaging where recipients can reply to the number that texted them and the sender's software receives and acts on those replies.
- Webhook: A webhook is an HTTP request a service sends to a URL you own when something happens, so your code learns about an inbound SMS or a delivery event the moment it occurs instead of polling for it.
Sources
- STOP keyword, api.ctia.org, checked on September 4, 2026