This page is part of the Customer.io documentation. For the complete documentation index, see llms.txt.

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SMS sender numbers

When you connect an SMS provider, we sync your sender identities—phone numbers, short codes, and sender IDs. This page explains how to manage your senders so you can select different senders for different messages.

Your senders come from your SMS provider: we sync the phone numbers, short codes, and sender IDs you’ve set up with your provider, and you pick one when you compose a message. How you manage them depends on your provider.

Syncing phone numbers (senders) to Customer.io

If you add or change any of your sender identities, you’ll need to re-sync them in Customer.io before you’ll see your changes in Customer.io.

Go to > Workspace Settings > SMS and click Sync from Twilio.

Senders through Twilio

Twilio has its own sender settings around auto-syncing and manual sender IDs that are unique compared to other SMS providers.

Hide auto-synced sender identities

When you sync from Twilio, Customer.io automatically imports all of your sender identities. If you don’t want to use some of these auto-synced senders, you can hide them. Hiding a sender moves it to a separate Hidden tab on your SMS settings page and prevents it from appearing as an option when you draft a message. Hiding a sender doesn’t remove it from Twilio—you can unhide it at any time to make it selectable again.

Go to > Workspace Settings > SMS and click Hide next to sender identities you don’t want to use.

Using a Manual Sender ID

You’ll see Manual Sender IDs in your Twilio Settings. You can add an Alphanumeric Sender ID, a Message Service ID, or provide some Liquid that dynamically determines the Sender ID for each message here. Manual sender IDs are only available for accounts integrated with Twilio before July 30, 2026.

Alphanumeric ID

Alphanumeric IDs can help your messages stand out, but they have a few quirks:

• They’re one-way: Your customers cannot reply to them.
• Opt-in/opt-out: Customers must opt into messages from your ID, and be informed on how to opt out.
• Alphanumeric IDs aren’t supported in all countries, including the USA: If you try to send to an unsupported country from an Alphanumeric Sender ID, your message will fail to send.

Set up an alphanumeric ID

1. Enable alphanumeric IDs in Twilio first! You can add alphanumeric senders in Customer.io, but if you haven’t enabled the feature in Twilio, messages using your alphanumeric sender will fail.

2. Go to > Workspace Settings > SMS and click Add Sender ID.

3. Enter your Sender ID and the Name you’ll use to refer to your sender.

   • Name: this is how you’ll refer to the ID internally; your customers won’t see this.
   • Sender ID: You can use both upper- and lower-case ASCII letters, digits 0 through 9, and spaces in your ID. Your ID must contain at least one character that isn’t a number.