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


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

Applies To

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


The opt-out flow for US toll-free numbers is mandated by US carriers and is 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" 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.
  5. User STOP and UNSTOP requests are forwarded back to users.
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