How is opt-out managed when sending SMS from a US toll-free number?

Question

What happens when a user sends STOP to my toll-free number?

Applies To

• Toll-Free Numbers
• Outbound SMS
• Opt-Out
• US Carriers

Answer

The opt-out flow for US toll-free numbers is managed at a network level and is enforced by the US operators. The service can not be disabled. It works as follows:

1. A user sends the word STOP to the toll-free number.
2. The carrier sends the following outbound message to the user: NETWORK MSG: You replied with the word "stop" which blocks all texts sent from this number. Text back "unstop" or "start" to receive messages again. 
3. Any subsequent MT messages sent from the toll-free number will fail with error code 9 and the message Illegal Number - you tried to send a message to a blacklisted phone number. That is, the user has already sent a STOP opt-out message and no longer wishes to receive messages from you.
4. If the user wishes to re-subscribe to the service, they can send a new message to the toll-free number with the word UNSTOP or START.
5. User STOP, UNSTOP and START requests are forwarded back to users.