Build Your SMS Opt-In List

  • Updated

Before you can send SMS to a recipient, they must consent to receive messages. The SMS Opt-In List is the record of that consent, and Act-On only sends to numbers on it. This article covers the three ways to build the list and the one-time first-message flow that runs when you go live.

Who does this: Marketing ops and demand gen teams; legal or compliance often weigh in on disclaimers and data handling
Time needed: 5 minutes to orient; the actual work depends on which route you take
Why this matters: SMS is strictly opt-in. Messaging numbers that didn't agree to hear from you exposes your business to regulatory fines, carrier blocks, and lawsuits. An accurate, well-maintained Opt-In List is the foundation that keeps the channel working.
In plain English: You have three ways in - a Form with a drop-in SMS Opt-In section, a custom Form you map yourself, or an upload from somewhere else. Once numbers are on the list, Act-On takes care of checking every send against it.

Three ways to build your SMS Opt-In List

1. Add the SMS Opt-In section to a Form

The fastest path. Drag and drop the pre-built SMS Opt-In section into an Act-On Form. It includes a Phone Number field, an opt-in checkbox with disclaimer, reCAPTCHA, and a Submit button - all pre-mapped to the Opt-In List.

Best for: teams that want Act-On to handle the technical mapping and compliance scaffolding. Not available for classic Forms.

Walkthrough: Add SMS Opt-In to a Form.

2. Build a custom SMS Opt-In Form

Design your own Form that collects phone numbers and opt-in consent. Route submissions to a Form Submission list, then map that list as an Opt-In source.

Best for: teams that need Form designs the SMS Opt-In section doesn't accommodate. If your account does not yet have SMS Credits, you can still collect opt-ins this way and map the list once Credits are in place.

Mapping walkthrough: Add SMS Opt-Ins from a Marketing List or External Data Source - Step 2.

3. Upload opt-ins from an external data source

If you are transferring SMS marketing from another provider, you likely already have an opt-in list. Upload it as an Act-On Marketing List and add that list as an Opt-In source.

Best for: migrations and bulk imports. See Add SMS Opt-Ins from a Marketing List or External Data Source.

Your first SMS Opt-In Message

If you arrive at SMS in Act-On with contacts who already opted in (via a Form, an earlier provider, or an import) but haven't yet received a message from your Act-On sending number, Act-On prompts you to send a one-time opt-in confirmation the first time you visit SMS > Messages. Every contact in your SMS Opt-Ins receives it once.

Prerequisites: Your account has SMS Credits, and you have at least one contact in your SMS Opt-Ins. You only see this prompt if both are true and you haven't sent from SMS before.
  1. Go to SMS > Messages. If this is your first visit, you are prompted to send your first opt-in message.
  2. Click Set Up Now.
  3. In the SMS Message Composer, write a short confirmation message for your existing opt-ins:
    • Click simple or legalese to start from a template.
    • Click the calendar icon to insert the opt-in date: {{={{_TIME(20)}}}}
    • The "Txt STOP to OptOut" disclosure is required and cannot be removed.
  4. In the Message Preview, pick a recipient from the dropdown to see how the final message will look.
  5. Click Send Message to send now, or Schedule Send to pick a date and time.

After a few minutes the message sends and appears in SMS > Messages. Once your first message is out, you can set up your automated Welcome Message for future opt-ins.

Maintaining the Opt-In List

  • Contacts who submit a Form with the SMS Opt-In section are added automatically.
  • Contacts added to an already-mapped Marketing List are added automatically.
  • Numbers that reply STOP are moved to the Opt-Out List. They can return by replying START.
  • Opting out of SMS is separate from Email Opt-Outs - the two lists don't share state.

Next steps

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