Retrieve SMS Message Opt-outs (heuristic)

Returns SMS subscription addons that (a) actually received this message and (b) ended within the OPT_OUT_WINDOW_HOURS time window after the message was sent. The recipient-of-this-message filter implicitly scopes to the messaging service the message was sent from. The time window is heuristic because Twilio's inbound STOP path does not record which message triggered the reply.