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Twilio Support for Opt-out Keywords (SMS STOP Filtering)

Overview

By default, Twilio handles standard English-language reply messages such as STOP, UNSUBSCRIBE, STOPALL or CANCEL for Toll-Free and Long Code messages, in accordance with industry standards. 

Notice regarding Unified Cross Channel Opt-Outs: Starting Mon Mar 16, 2026, Twilio automatically unifies opt-out management across RCS, SMS, and MMS channels. If an end-user replies with  opt-out keywords (like STOP, QUIT, CANCEL etc) to an RCS message, Twilio will automatically block future SMS or MMS messages sent from that same Sender or Messaging Service (and vice versa), returning Error Code 21610. This synchronization is active by default to protect your sender reputation and requires no code changes.

Notice regarding messaging fees: Standard messaging fees apply to the original inbound STOP/START/HELP/INFO message that is being sent to your Twilio number, in the same manner as any other inbound SMS message. However, there are no additional fees for the blocklist changes triggered by these keywords, and no cost for the automatic reply to the sender.

Notice: Text message campaigns may be subject to various legal compliance requirements depending on the nature of your text messaging campaign, the location from where you are sending your text messages, and the location of your recipients. While Twilio will handle the above-described messages on long codes and Toll-Free numbers in the way described in this article, you should consult with your legal counsel to ensure that your text messaging campaign conforms to all applicable legal compliance requirements. If you have further questions on this, please contact Twilio Support.

 

What You Need To Know

Advanced Opt-Out for Messaging Services 🔗

Customers using Twilio's free Messaging Services feature can also customize opt-in/out keywords and replies by using Advanced Opt-Out. For more information, see the following resources:

STOP, STOPALL, UNSUBSCRIBE, CANCEL, END, REVOKE, OPTOUT or QUIT 🔗

Default reply: You have successfully been unsubscribed. You will not receive any more messages from this number. Reply START to resubscribe.

Any of these STOP keyword replies will prevent a customer from receiving new messages from the Twilio phone number they're responding to. When Twilio receives one of these replies, we will create a "block list" entry on our side, and then pass the message on to your webhook. Once we have a block list entry for a particular recipient phone number, any future attempts to message them will be met with a 400 response from our API, along with Error Code 21610 - Message cannot be sent to the 'To' number because the customer has replied with STOP. Recipients can disable this message stop, and resume receiving messages with the START, YES, or UNSTOP commands as outlined below.

Only single-word messages will trigger the block. So, for example, replying STOP will stop the customer from receiving messages from that particular Twilio number, but replying "STOP PLEASE" or "PLEASE CANCEL" will not. Further, the block works and is logged even if your number currently has no messaging request URL.

Please note that these STOP keyword replies only apply to the most recent number that messaged the recipient. If you are using more than one Toll-Free number or Long Code for sending messages, you must take additional action separate from Twilio to prevent these customers from receiving messages from your other numbers. We recommend blocking numbers on your side when one of these message responses is received at your webhook.
 

START, YES and UNSTOP 🔗

Default reply: You have successfully been re-subscribed to messages from this number. Reply HELP for help. Reply STOP to unsubscribe. Msg&Data Rates May Apply.

Any of these replies will opt customers back in to the messages coming from a Twilio Long Code. These messages will also be delivered to your Twilio account, and the defined web hook, so you can update your application logic.

Notice: Twilio Toll-Free numbers only respond to START and UNSTOP for re-subscribe. Twilio cannot disable the STOP/UNSTOP replies for Toll Free Numbers. Even if Advanced Opt Out is enabled, end users will continue to receive the "Network MSG". Learn more here Opt-out keyword handling (SMS STOP Filtering) for Toll-Free SMS


HELP and INFO 🔗

Default reply: Reply STOP to unsubscribe. Msg&Data Rates May Apply.

These keywords should return basic helpful information, such as how to opt out. If you customize your keyword responses using Advanced Opt-Out, we recommend incorporating your business name in this reply as well.

Notice for U.S/CA Toll-Free Twilio numbers, if a recipient has opted out of SMS from your number, any Help/Info replies will not be delivered unless they opt back in first. For more information, see Opt-out keyword handling (SMS STOP Filtering) for Toll-Free SMS

Twilio does not forward HELP/INFO messages to your incoming message webhook by default. However, if you use Advanced Opt-Out for Messaging Services, Twilio does forward HELP/INFO requests to your inbound webhook. For more information, see Getting Started with Advanced Opt-Out for Messaging Services
 

Messaging Services 🔗

When sending messages, you can specify for the ‘from’ parameter either a valid sender on the Account (e.g. Phone Number, Short Code, Alphanumeric Sender ID, RCS, WhatsApp Sender) or a valid Messaging Service SID on the account. If a Messaging Service SID is specified then Twilio’s Sender Selection service will automatically choose the best sender within that service for the ‘to’ number.

Any STOP keyword replies sent to a phone number that is part of a Messaging Service will create two opt-out records within Twilio: one for the phone number that received the opt-out and one for the Messaging Service. This opt-out record for the Messaging Service allows end user opt-outs to be respected when the Messaging Service’s Sender Selection feature is being used.

The opt-out record for the Messaging Service only applies in scenarios where you are specifying the Messaging Service SID in your API calls in place of a Sender. If you are not using the Sender Selection feature of the Messaging Service then the opt-out will only apply to the number that received the opt-out; any other senders within the service will not be blocked from sending messages to that recipient.

Note that users’ START replies must be sent toward the same sender ID that they originally sent the STOP message toward in order for re-subscribe to function correctly.

It is possible to customize opt-out keywords and responses for a Messaging Service. For example, you can change the default keywords and replies, and add support for additional languages.

Lastly, Twilio will add an additional parameter to the inbound webhook payload for opt-ins and opt-outs if you enable Advanced Opt-Out for Messaging Services. This field is called OptOutType and allows you to track opt-in and opt-out responses based on the keyword the sender used, instead of having to monitor for all START/STOP keyword variants on your server (such as cancel, quit, etc.). 

For more information, see Getting Started with Advanced Opt-Out for Messaging Services.
 

Short Codes 🔗

By default, Twilio will not handle opt-out, opt-in or help keywords for short code numbers, unless the short code has been added to a Messaging Service and Advanced Opt Out enabled.

If you are using a Messaging Service, you can configure your keywords using Advanced Opt-Out to match the compliant opt-out, opt-in and help message language from your short code application. You can also choose to disable Twilio’s keyword handling altogether and use your own system.

It is very important to ensure that your short code is compliant to all industry rules and regulations for opt-out handling. For detailed information on short code HELP and STOP responses, please see Industry Standards for US Short Code HELP and STOP.
 

Alphanumeric Sender ID 🔗

Alpha Sender IDs are for one-way messaging only, and are unable to receive inbound messages. As a result, Twilio’s SMS STOP, START, HELP keywords are not applicable for Alpha Sender IDs. You must provide other instructions, such as writing a Support team, calling a Support phone line, or texting another phone number or code to allow users to opt out from messages sent via Alpha Sender ID.

RCS 🔗

By default Twilio will handle standard opt-out, opt-in, or help keywords for RCS Senders. When using a Messaging Service, you can customize opt-in/out keywords and replies by using Advanced Opt-Out. 

RCS supports various Rich Content message types, so be aware that replies sent with Rich Content types such as quick replies will trigger keywords and honor opt-out. 

 

Frequently Asked Questions

How to check Opt Outs on your account?

You can check opt outs in the Messaging Insights section of the Twilio Console. See here for more information.

How to use the OptOutType parameter to track opt-in and opt-out responses?

See this article for more information on how to use the OptOutType parameter available in Incoming Message Webhooks for Advanced Opt Out, or on Event Streams for all incoming messages.

Can default STOP filtering be disabled?

Yes, default STOP filtering can be disabled at the account level.  This implies STOP filtering must be managed completely on the side of the customer.  Please contact Twilio Support if you would like to request this.

Is there an API that I can use to manage opt-ins and opt-outs within Twilio’s platform?

Yes, please see the Consent Management API within the Compliance Toolkit product.

 

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