What is SMS opt-in and STOP?
The documented agreement a recipient gives before receiving texts, and the universal keyword that withdraws it at any time.
SMS opt-in — SMS opt-in is the recipient's documented agreement to receive text messages from a business, and STOP is the universal keyword that withdraws it; carriers and the TCPA require both to be honoured. The opt-in record is what a business shows when challenged.
Also known as: SMS consent
Why it matters
Sending a business text to someone requires their agreement first, and that agreement has to be more than assumed. Opt-in means the recipient took a specific, documented action, checking a box, replying YES, submitting a form that clearly says texts will follow, and the business keeps a record of when and how that happened. Without that record, a business has no way to demonstrate consent if a recipient disputes ever agreeing to receive texts.
STOP is the other half of the same rule. Every recipient has to be able to withdraw consent at any time by replying STOP, and carriers and the TCPA require that withdrawal be honoured immediately, no further messages after that point. A business that keeps texting someone who replied STOP is violating the same framework that required opt-in in the first place, and carriers actively watch for exactly this pattern.
What a compliant opt-in flow looks like
- 1
The recipient is told texts will be sent
A form or sign-up flow clearly discloses that SMS messages will follow, not buried in fine print.
- 2
They take a specific action to agree
Checking a box, replying YES, or another explicit step, not only supplying a phone number.
- 3
The opt-in is recorded
Timestamp and method are logged against the contact, kept as evidence of consent.
- 4
STOP is honoured immediately
A reply of STOP ends further messages to that number without delay.
The mistake to watch for
Questions
- What is the difference between SMS opt-in and email opt-in?
- Both require documented consent, but SMS carries stricter, carrier-enforced rules around the STOP keyword and how quickly it must be honoured, along with registration frameworks like 10DLC that email doesn't have. A phone number supplied on a form is not, by itself, opt-in the way it might loosely be treated for email.
- Does collecting a phone number count as SMS opt-in?
- No. A phone number alone does not establish consent to text it. The recipient needs to take an explicit action, after being told texts will follow, for that to count as a documented opt-in.
- What has to happen when someone replies STOP?
- Further messages to that number have to stop immediately. This is a requirement carriers and the TCPA both enforce, and the record of the STOP reply should be kept the same way the original opt-in was. This is not legal advice.