The Cellular Telecommunications Industry Association (CTIA) guidelines require that businesses sending application to person (A2P) text messages support the standard keywords STOP, HELP, and START, and respond automatically to each one. Network carriers require an automatic response to every STOP and HELP request, even repeat requests. For example, if a customer texts STOP twice, you should still send the opt-out confirmation even though the first STOP request would place the customer on a Do Not Call (DNC) list. You must reply to a STOP request even if the customer has already reached the maximum attempts permitted by Attempt Supervisor. 

If a customer opts out of receiving SMS messages, you cannot send an SMS outside of the START/STOP/HELP auto-responses. If the customer asks a questions, do NOT respond using SMS, you should switch to another channel (phone or email). Customers using a virtual assistant on their inbound SMS flow should add a DNC-check module before the virtual assistant replies so no non-START/STOP/HELP messages are sent once a customer has opted out. 

Attempt Supervisor and DNC status are not automatically checked. To ensure that the DNC status is checked, you should add a module to your contact flow using the DNC APIs. There is currently no API to check Attempt Supervisor status from a contact flow. 

For additional information, see Working with Contact Flows, Compliance API, Creating and Deploying a Contact Flow.