Carriers maintain network-level opt-out lists. Failing to honor STOP keywords incurs immediate $10,000 regulatory penalties and route termination.
When a recipient replies STOP to any commercial SMS, carrier networks automatically blacklist the sender number from messaging that subscriber. Telephony applications must synchronize this state immediately to avoid sending subsequent messages that result in carrier fines.
1 Universal Opt-Out Keywords
Under CTIA guidelines, applications must honor all variations:
- Opt-Out: STOP, STOPALL, UNSUBSCRIBE, CANCEL, END, QUIT.
- Opt-In Reversal: START, UNSTOP, YES.
- Information: HELP, INFO.
Frequently Asked Questions • Carrier Spam Filters & Deliverability
Yes. Carriers explicitly permit exactly one single automated confirmation message: 'You have unsubscribed and will receive no further messages. Reply HELP for info.'