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.

If Customer.io manages SMS for your account, your senders are already in your workspace, and your connection appears as SMS rather than under a provider’s name. You don’t need to “sync” anything.

Sync your senders to Customer.io

If you add or change any of your sender identities with your provider, you need to sync them to Customer.io before you can use them.

1. Go to > Workspace settings > SMS settings.
2. Click Manage next to the connection you want to sync.
3. Click Sync sender identities.

Hide senders you don’t want to use

When you sync senders, Customer.io imports every sender identity on your provider account. If you don’t want to use some of these senders, you can hide them. When you hide a sender, you and your team members can’t use it to send messages.

1. Go to > Workspace settings > SMS.
2. Click Manage next to the SMS provider containing the sender.
3. Click > Hide sender identity for the sender you want to hide.

The sender moves to the Hidden tab. You can’t hide a sender while it’s used by a dynamic sender.

Hiding a sender in Customer.io doesn’t change anything with your provider. To make a hidden sender selectable again, go to the Hidden tab, click > Show sender identity for the sender you want to show, and click Save.

Rename senders

You can rename a sender to give it a name your team recognizes, like Support line or Marketing.

1. Go to > Workspace settings > SMS.
2. Click Manage next to the SMS provider containing the sender.
3. Click > Edit name… for the sender you want to rename.
4. Enter a new name and click Save name.

The new name only changes how the sender appears in Customer.io. Resyncing senders doesn’t change the name you set.

Dynamic senders

A dynamic sender lets you create a single sender profile that uses different phone numbers based on the country code in each recipient’s phone number. For example, you might create a dynamic sender that texts UK phone numbers from your UK sender, Irish numbers from your Irish sender, and everyone else from your US toll-free sender.

A dynamic sender saves you the trouble of creating separate messages for each sender and helps you keep your audience’s opt-out status consistent.

You manage dynamic senders on the Senders tab of your SMS settings page. A dynamic sender can route to any sender on any of your providers. If Customer.io manages SMS for your account, that includes the senders Customer.io set up for you.

If you connected Twilio before July 30, 2026 and send through the Twilio Actions page, you can’t use dynamic senders. Messages sent through that integration always send from the number you pick.

Create a dynamic sender

1. Go to > Workspace settings > SMS > Senders.

   

2. Under Dynamic senders, click Add dynamic sender.

   

3. Enter a Name for your dynamic sender. You’ll see this name when you pick a sender for a message. Your audience doesn’t see it.

4. Under Countries, set up at least one group. Choose the Countries in the group. Then, under Send from, pick the Sender identity your messages come from, or choose Don’t send to skip them. Click Add countries to add another group.

5. Under Default, pick the Default sender identity for recipients whose country isn’t in any group—or choose Don’t send.

6. Under Numbers without a country code, choose an Assumed country. Customer.io reads phone numbers without a country code, like 07400 123456, as numbers from this country. The default is the United States.

7. (Optional) Under Test a number, enter a recipient’s phone number and click Test. Customer.io shows which sender we would use for that phone number. This doesn’t send a message.

8. Click Add dynamic sender.

Each country can belong to only one group, so the order of your groups doesn’t matter.

Send a message with a dynamic sender

When you write an SMS message, choose your dynamic sender in the From field. Dynamic senders appear in their own group in the list, separate from your phone numbers.

When Customer.io sends the message, it checks the recipient’s phone number and sends from the sender identity for that recipient’s country:

• The country code decides the country. For example, a recipient with a +353 number gets the sender for Ireland.
• Numbers without a country code use your assumed country.
• Countries that aren’t in any group, and numbers Customer.io can’t place in a country, use your Default setting.

Some places share a country code but count as separate countries. The United States and Canada both use +1; Customer.io tells these numbers apart by area code. Similarly, numbers from Guernsey, Jersey, and the Isle of Man start with +44, but they don’t match a group that contains only the United Kingdom. You can add those countries to the group if you want them to get your UK sender. Use Test a number to check how a specific number routes.

Your delivery details show the number Customer.io sent from, followed by the name of the dynamic sender that picked it.

If a recipient’s country is set to Don’t send, Customer.io doesn’t send them a message. The message’s status is undeliverable, and its reason names the dynamic sender and the recipient’s country.

Opt-outs and dynamic senders

When someone replies STOP to any number in a dynamic sender, Customer.io opts them out of that whole dynamic sender. Customer.io stops texting them from every number in the dynamic sender, as well as from any other dynamic sender that includes the number they replied to. This way, a person who opts out doesn’t start receiving your texts from a different number in the same dynamic sender.

The opt-out covers the number the person replied to and the dynamic senders that include it. If you send a message directly from one of the dynamic sender’s other numbers, without using the dynamic sender, the person still receives it.

Opting back in works the same way. When the person texts START to the number they opted out from, or when you remove the opt-out for that number on their profile, Customer.io opts them back in to the number and to every dynamic sender that includes it. See opt-out keyword handling for more about opt-outs.

Keep your dynamic senders up to date

If you remove a number from your provider and sync your senders, any dynamic sender that used that number shows Action required. Edit the dynamic sender and select another sender identity for the affected countries. Until you do, messages to recipients in those countries fail.

You can’t delete a dynamic sender while a message uses it. To find the messages that use it, open the dynamic sender’s menu and select View usages. Change the sender in those messages first.

Manual sender identities

In general, you’ll sync your senders from your SMS provider. However, you can also add senders manually. You might do this for:

• Senders that use liquid : this lets you pick a sender for each message based on the context of the message. See Dynamically render a sender for examples. To pick a sender based on the recipient’s country, use a dynamic sender instead.
• Alphanumeric sender IDs and other static values that can’t be synced from your provider: If you want to add a sender this way, your provider has to accept the value you enter. This often means you’ll need to set up the sender value with your provider first. For example, you might enable alphanumeric sending in Twilio ↗.

To add a manual sender, go to > Workspace settings > SMS > Senders. Under Manual senders, click Add manual sender.

When you add a manual sender, you choose the Provider credential that sends it. If you’ve connected more than one provider, you can choose Automatic instead: Customer.io renders the value and matches it against your synced senders to decide which provider to use. With Automatic, the rendered value must match one of your synced senders.

Alphanumeric sender IDs

Alphanumeric sender IDs, like InfoSMS, let you send from your brand name instead of a number.

Customer.io syncs alphanumeric sender IDs from Infobip and Twilio:

• Infobip: register the ID with Infobip and it syncs alongside your numbers. See Set up SMS with Infobip.
• Twilio: add the ID to a Messaging Service in Twilio and it syncs alongside your numbers, short codes, and Messaging Services. Synced IDs appear as <ID> (Alphanumeric)—for example, ACME (Alphanumeric). You’ll only see the ID once, even it belongs to more than one Messaging Service. See Set up SMS with Twilio for more details.

On any other connection—or for an ID that isn’t on a Twilio Messaging Service—add the ID as a manual sender identity. Your provider has to support alphanumeric senders, and some require you to enable or register the ID first.

Alphanumeric senders come with a few constraints:

• They’re one-way: people can’t reply to them, so opt-out keywords like STOP never reach you. You must give your audience another way to opt out.
• People still need to opt in: recipients must consent to messages from your sender ID, and you must tell them how to opt out.
• Country support varies: many countries—including the United States—don’t allow alphanumeric senders, and some require you to register the sender first. Check your provider’s coverage for the countries relevant to your audience and business.

If you connected Twilio before July 30, 2026

Older Twilio integrations have their own settings page, Twilio Actions. It works a little differently from the SMS page.

To sync senders, go to > Workspace settings > SMS and select Sync from Twilio.

Manual sender IDs

Under Manual Sender IDs, you can add an alphanumeric sender ID, a messaging service ID, or Liquid that picks the sender ID for each message. See an example of a Liquid sender.

Add an alphanumeric sender ID

1. Enable alphanumeric IDs in Twilio ↗ first. You can add alphanumeric senders in Customer.io, but messages using them fail until you enable the feature in Twilio.

2. Go to > Workspace settings > SMS and select Add Sender ID.

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

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