SMS Opt-Out Management

Manage opt-out (STOP) handling, consent records, and TCPA compliance for outbound SMS campaigns. Non-compliance risks $500-$1,500 per unsolicited message in TCPA fines.

TCPA Requirements for B2B Cold SMS

1. Prior express consent is required for non-marketing informational texts. For marketing texts, prior express written consent is required.
2. B2B cold SMS to business numbers is a gray area. Mitigate risk by:
   • Sending only to business-registered mobile numbers
   • Including opt-out instructions in every first message
   • Honoring STOP requests immediately (within seconds, not hours)
   • Maintaining a suppression list
   • Keeping messages relevant and non-promotional in tone
3. Never send before 8am or after 9pm in the recipient's local timezone.

Twilio (Default)

Automatic STOP handling

Twilio's Messaging Service has built-in Advanced Opt-Out enabled by default. When a recipient replies STOP, STOPALL, UNSUBSCRIBE, CANCEL, END, or QUIT, Twilio:

• Automatically replies with a confirmation message
• Blocks future messages to that number from your Messaging Service
• Returns error 21610 if you attempt to send to an opted-out number

Verify opt-out is enabled:

curl "https://messaging.twilio.com/v1/Services/$TWILIO_MESSAGING_SERVICE_SID" \
  -u "$TWILIO_ACCOUNT_SID:$TWILIO_AUTH_TOKEN"

Check use_inbound_webhook_on_number and ensure opt-out handling is not overridden.

Query opt-out list

There is no direct API to list all opted-out numbers. Instead, attempt a send and catch error 21610, or maintain your own suppression list synced from webhook events.

Webhook for opt-out events

Configure a status callback URL on your Messaging Service. When a STOP is received, Twilio fires a webhook with OptOutType=STOP. Capture this in n8n and:

1. Mark the contact as sms_opted_out=true in Attio
2. Add the phone number to your suppression list
3. Log a sms_opt_out event in PostHog with properties: phone_number_hash, campaign_id, opt_out_keyword

Re-opt-in

If a contact replies START or UNSTOP, Twilio automatically re-enables messaging and fires a webhook with OptOutType=START. Update the contact record in Attio accordingly.

Salesmsg

Opt-out handled automatically. Salesmsg maintains a global do-not-contact list per account. When someone texts STOP, they are blocked from all future messages. Access the suppression list via dashboard > Contacts > Opted Out.

OpenPhone (Quo)

Opt-out handling is automatic for registered A2P numbers. STOP replies trigger carrier-level blocking. Quo surfaces opt-out events in the conversation thread.

Suppression List Management

Regardless of provider, maintain a master suppression list in your CRM (Attio):

1. Create a custom attribute sms_opted_out (boolean) on the Person object
2. Create a custom attribute sms_opt_out_date (date) on the Person object
3. Before every SMS send, query Attio to verify the contact has sms_opted_out != true
4. Sync the suppression list bidirectionally: provider opt-outs update Attio, Attio manual opt-outs update the provider (where API allows)

Pre-Send Compliance Checklist

Before sending any SMS in this play, verify:

• [ ] A2P 10DLC registration is active and approved
• [ ] STOP handling is enabled on the messaging service
• [ ] First message to any new contact includes "Reply STOP to opt out"
• [ ] Sending window is 8am-9pm in recipient's timezone
• [ ] Contact is not on the suppression list
• [ ] Phone number is a mobile number (landlines cannot receive SMS)