Opt-out keyword handling is one of the most operationally overlooked areas of SMS compliance, despite the fact that getting it wrong creates immediate and concrete legal exposure. The CTIA Messaging Principles and Best Practices, which carriers enforce as a condition of A2P 10DLC registration, require that senders respond to opt-out keywords immediately with a confirmation message, cease all further messaging to that number, and provide a mechanism for re-subscription. Failing to honor a STOP reply is a per-message TCPA violation for every subsequent message sent to that number.
The Required Response to STOP and Similar Keywords
When a subscriber replies STOP, END, CANCEL, UNSUBSCRIBE, or QUIT to any of your Twilio numbers, you are required to immediately send a single confirmation message and then cease all further messaging to that number until they explicitly opt back in. The confirmation message must state that the subscriber has been unsubscribed and will no longer receive messages, must not contain any promotional content, and should be under 160 characters. An example compliant response is: You have been unsubscribed from [Business Name] messages. No further messages will be sent. Reply START to resubscribe. Twilio's messaging services handle opt-out keyword detection automatically, but only if your Twilio Messaging Service has opt-out management enabled, which must be explicitly configured in your Messaging Service settings.
What HELP Must Return
When a subscriber replies HELP, your system must return a message that includes your business name or program name, a brief description of the messaging program, contact information for customer support such as a phone number or email address, and opt-out instructions. A minimal compliant HELP response looks like: [Business Name] Alerts: For support, contact support@yourbusiness.com or call 1-800-XXX-XXXX. Reply STOP to unsubscribe. Msg & data rates may apply. The HELP response must be configured in your Twilio Messaging Service and tested to confirm it sends correctly. Subscribers who receive a HELP reply that does not include support contact information or opt-out instructions have grounds to file a carrier complaint, which is weighted heavily in your A2P trust score calculation.
START and Re-Subscription Handling
When a previously opted-out subscriber replies START or UNSTOP to your number, they are expressing intent to re-subscribe to your messaging program. Under CTIA guidelines, you should respond with a re-subscription confirmation that mirrors your original opt-in confirmation, restating the program description, message frequency, and opt-out instructions. You must add the number back to your active list before any further messages are sent after the START reply, not batch-process re-subscriptions overnight. In Twilio's Messaging Services, re-subscription via the START keyword is handled automatically by the opt-in management feature, but you need to ensure that your downstream CRM or marketing platform is notified of the re-subscription event and updates its suppression list accordingly. A number that appears on your internal opt-out list but is re-subscribed in Twilio without the update propagating to your CRM will continue to be suppressed there, causing missed sends.
Building Keyword Handling That Works Across All Numbers
If you use multiple Twilio phone numbers to send messages under the same campaign, opt-out handling must work correctly across all of them, not just the primary sending number. A subscriber who replies STOP to one of your 10DLC numbers expects to be unsubscribed from your program entirely, not just from that one number. Implement a centralized opt-out database that your Twilio webhook handler writes to whenever a STOP keyword is received on any number in your pool, and check this database before every send regardless of which number initiates the message. Additionally, opt-out records should be stored indefinitely or for a minimum of four years to align with TCPA litigation timelines. Audit your opt-out handling quarterly by sending test STOP replies to each active sending number and verifying that the confirmation response is received and that subsequent messages are blocked.
Conclusion
Keyword handling is a compliance obligation that must work flawlessly every time, not something that can be addressed through best-effort implementation or periodic cleanup. Speak with our compliance team and we will audit your opt-out handling across every Twilio number in your account and fix any gaps.
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