Stop at the first STOP

How to do it

Accept at least STOP, QUIT, END, REVOKE, OPT OUT, CANCEL and UNSUBSCRIBE, in any case and with extra spaces. The FCC lists these as reasonable ways to revoke consent and requires you to honour them within 10 business days. Aim for seconds. Send at most one confirmation of the opt-out, within 5 minutes, with no marketing in it. Add the number to a suppression list your send code reads, because providers often block only their own copy. Accept START or UNSTOP to opt back in. The FCC rule that one STOP covers every message type from you is delayed until 31 January 2027, so check its status before then.

Example

const OPT_OUT_WORDS = new Set(['stop', 'quit', 'end', 'revoke', 'optout', 'cancel', 'unsubscribe', 'stopall']);
export const isOptOut = body => OPT_OUT_WORDS.has(body.trim().toLowerCase().replace(/[\s-]+/g, ''));

app.post('/sms/inbound', verifyProviderSignature, async (req, res) => {
  if (isOptOut(req.body.Body)) await db.smsSuppressions.add(req.body.From, req.body.To);
  res.sendStatus(204);
});

import re

OPT_OUT_WORDS = {"stop", "quit", "end", "revoke", "optout", "cancel", "unsubscribe", "stopall"}

def is_opt_out(body: str) -> bool:
    return re.sub(r"[\s-]+", "", body.strip().lower()) in OPT_OUT_WORDS

@app.post("/sms/inbound")
def inbound_sms():
    verify_provider_signature(request)
    if is_opt_out(request.form["Body"]):
        db.sms_suppressions.add(request.form["From"], request.form["To"])
    return "", 204

How to check

Text "stop " and "Opt out" from a test phone. Each gets one confirmation within 5 minutes, and a send to that number is refused by your code. Text HELP and the answer names the brand and a support address.