By default, Twilio handles HELP, STOP and certain other keywords when users text them into your Twilio ten-digit phone number. This is to help ensure that your app complies with recommended practices for the commercial use of SMS. For details, please see this page in our FAQ. We do not have a way for developers to customize the specific replies used in SMS filtering for ten-digit phone numbers. If you have further questions about this, just contact us.
Twilio does not handle your short code’s HELP & STOP replies, or your opt-out list by default. You should build this functionality into your own short code messaging application. For information on carriers’ requirements for short code HELP and STOP replies, please see this article.