STOP / HELP Keywords
Industry-standard SMS keywords that consumers reply with to opt out (STOP) or request information (HELP). All A2P senders must process them automatically.
STOP and HELP are the carrier-mandated SMS keywords that every A2P sender must support:
- STOP (and variants: END, CANCEL, UNSUBSCRIBE, QUIT) immediately opts the recipient out and triggers a confirmation message.
- HELP (and INFO) returns a contact message naming the brand and a way to reach support.
Failing to handle these keywords correctly is grounds for carrier suspension and is a frequently cited TCPA violation. Most modern messaging platforms (Twilio, GHL, Bandwidth) handle them automatically — but the brand is responsible for confirming the behavior.
Related glossary terms
Under TCPA, consumers can revoke SMS consent at any time by any reasonable means. Senders must honor the revocation — typically by adding the number to a suppression list — within 10 business days.
A suppression list is the registry of phone numbers that have revoked consent. Senders must check this list before every outbound send to remain TCPA-compliant.
10DLC (10-Digit Long Code) is the US carrier-mandated framework for sending Application-to-Person SMS from local 10-digit numbers, requiring brand and campaign registration with The Campaign Registry.