Spain SMS and RCS Sender ID Registration

Spain's telecommunications regulator (CNMC) now requires all businesses sending SMS or RCS to Spanish phone numbers using a branded (alphanumeric) sender ID to register that sender ID in a national registry. Starting September 15, 2026, any unregistered sender ID will be blocked in real time by Spanish carriers, meaning your SMS and RCS campaigns and flows will not reach Spanish recipients until registration is complete. Klaviyo will proactively block traffic to preserve your messaging credits and your deliverability.

This article explains your two options for getting registered, what you'll need, and how to decide which one is right for your account.

Is my account affected?

You are affected if both of the following apply:

• You send SMS and/or RCS to recipients with Spanish phone numbers (+34)
• You use an alphanumeric (branded) sender ID and/or an RCS sender — for example, "YourBrand" — rather than a short code or long code.

Using the same brand name for SMS and RCS? You need a separate registration for each channel. Registering your SMS sender ID does not cover your RCS sender ID.

Not affected: Numeric sender IDs (short codes and long codes) are outside the scope of this regulation and do not require registration.

If you're unsure which sender ID type your account uses, check Settings > Text message > Sender information in Klaviyo.

Your two options

You only need to complete one of the following, not both.

What you need to register

Both options require your sender ID, company details, and a legitimate connection to the sender name. The representative and document requirements differ: direct registration uses your legal representative and digital certificate, while the Klaviyo SMS form asks you to authorize Infobip to represent you. Have the relevant information ready before you start. Incomplete or incorrect submissions are a common reason for rejection.

Your sender ID

• Sender ID name: the branded name you send SMS or RCS from in Spain. SMS sender IDs must be 3–11 characters; RCS sender IDs can be 3–40 characters.
• Allowed characters: letters a-z, A-Z (including ñ and ç), numbers 0-9, space, @, &, -, _, ., +
• Not allowed: purely numeric strings, accented vowels (á, é, í, ó, ú), or special characters such as !, ?, #, %, *, (, )

Your company details (alias holder)

• Holder type: whether you are registering as a Legal Entity (company) or Natural Person (individual)
• Registered name: your official company name (Legal Entity) or first name + surname(s) (Natural Person)
• Tax ID:
  • Legal Entity registered in Spain: your Spanish company tax ID (NIF / CIF)
  • Natural Person: your Tax ID, NIE, or passport number for direct registration; your passport number for the Klaviyo SMS form.
  • Companies registered outside Spain: in Klaviyo's SMS form, select the registration type available for your country and enter your registration number. For direct CNMC registration, provide a NIF or valid EU VAT ID where possible. If you have neither, contact Klaviyo Support before submitting.
• Registered address and country

Your legal representative for direct registration

The details required depend on whether your representative is an individual or a company.

• If the representative is a Natural Person (individual): their Tax ID / NIE / Passport number, full name, surname(s), and email address
• If the representative is a Legal Entity (company): company tax ID and registered name, plus the details of the individual acting on its behalf: their Tax ID / Passport number, full name, and surname(s)

For direct registration, your legal representative will need to confirm the registration through the CNMC portal. See the digital certificate requirements below.

Proof of brand connection

You must demonstrate a legitimate connection between your company and the sender ID. Provide details of one of the following:

• Registered trademark (OEPM or EUIPO)
• Trade name or commercial name registration
• Corporate name registration
• Internet domain registered in your company's name

If none of the above apply, you may declare "habitual/legitimate use" and provide a written explanation of how and why you use the sender ID. The Klaviyo SMS form still requires the signed declaration and authorization letter described below.

Authorization letter for the Klaviyo SMS form

The Klaviyo SMS form requires a signed authorization letter appointing Infobip as your representative. Download the template provided in the form, complete and sign it, then upload it and confirm that you have signed it. You do not need your own digital certificate for this in-app SMS process.

Responsible Declaration document

For direct registration, a Responsible Declaration digitally signed by your legal representative is required. Contact Klaviyo Support to request the English or Spanish template. In the Klaviyo SMS form, download, sign, and upload the declaration provided for your sender ID, then select the confirmation checkbox.

Digital certificate for direct registration

For direct registration, your legal representative needs a valid digital certificate to access the CNMC portal and confirm the registration.

• Spanish companies use the FNMT certificate (issued by Spain's national mint and stamp factory)
• Non-Spanish companies (including US, UK, Australian, and other international businesses) need an eIDAS-qualified electronic certificate from a provider on Spain's Ministry of Economic Affairs approved registry (sedeaplicaciones.minetur.gob.es/prestadores/)

For non-EU companies specifically: the only internationally accessible provider currently confirmed on Spain's Ministry registry is Sectigo — look specifically for their Qualified Electronic Signature (QES) product; standard SSL or S/MIME certificates are not sufficient. Providers such as DigiCert, GlobalSign, Certigna, and D-Trust do not currently appear on Spain's Ministry registry, and certificates from them will not be accepted for this purpose.

EU-based companies can use their own country's national Qualified Trust Service Provider (QTSP), provided it appears on Spain's Ministry list.

Contact Klaviyo Support for guidance if you're unsure where to start.

Option A: Register directly with the CNMC

You submit your registration yourself through the CNMC's official portal. This gives you direct control over timing.

Two entries you must get right:

• Select Infobip as your Provider: this links your registration to Klaviyo's Spain sending infrastructure
• Add Klaviyo as a Third Party: Klaviyo's company name and Tax ID/registration ID are required here; see the full registration instructions for these details

Once submitted, the CNMC will contact your listed legal representative to confirm the registration. They have 10 business days to respond. If they miss this window, the registration will be rejected and must be resubmitted so give them a heads-up now so they know to expect it.

For a full field-by-field walkthrough, see our detailed guide: How to register your Spain SMS or RCS branded sender ID directly with the CNMC.

Notify Klaviyo of your direct registration

For an existing SMS sender that still needs registration in Klaviyo:

1. Go to Settings > Text message > Sender information. Find your Spanish sender, select Resolve, then Finish registering.
2. Select Yes, I already registered directly with CNMC, then Submit.
3. Review the confirmation, then select Close. Klaviyo will verify your registration and update your sender status.

For an RCS sender, contact Klaviyo Support with your sender ID and confirmation of direct registration. If the direct-registration choice is not available for your SMS sender, contact Support with your registration confirmation.

Option B: Register through Klaviyo

If you'd rather not manage the CNMC portal yourself, Klaviyo handles submission to the CNMC on your behalf.

Registering an RCS sender ID? The in-app form does not accept RCS sender IDs yet. Contact Klaviyo Support with your sender ID and company details from "What you need to register" above. Confirm the required documents with Support so Klaviyo can submit your registration on your behalf.

Registering a branded (alphanumeric) sender ID?

1. Open the Spain SMS registration form
2. If asked whether this sender has already been registered with the CNMC, select No, register through Klaviyo, then Next.
3. Enter your sender ID and select Next. Select a Legal basis for sender ID and enter the requested details linking it to your business, then select Next.
4. Enter your organization type, business or individual details, and registered address. Select Next.
5. Download, complete, sign, and upload the authorization letter and the declaration provided in the form. Select each confirmation checkbox and use Next to continue between steps.
6. Select Submit. Klaviyo passes your details and signed documents to Infobip for registration with the CNMC.
7. Review the confirmation, then select Close.

The CNMC reviews your registration. You'll receive an email notification when your registration is approved or rejected.

You can check your SMS sender registration status at any time under Settings > Text message > Sender information.

Klaviyo does not control the CNMC's review process or guarantee a completion date. Option A gives you direct control over when you submit, but the CNMC still determines when your registration is approved.

Which option should I choose?

• Choose Option A if you want to submit directly to the CNMC and manage the application yourself.
• Choose Option B if you'd prefer Klaviyo to manage the process for you and you're comfortable with some timeline uncertainty.

Registration statuses

For branded (alphanumeric) SMS sender IDs, open the sender details in Settings > Text message > Sender information to review the status.

Can I keep sending while registration is pending?

From September 15, 2026, branded SMS and RCS sender IDs must be registered to send to Spanish numbers. A registration in progress is not approval. For SMS, wait until your sender is approved and shows Active before sending with it. For RCS, wait for Klaviyo Support to confirm approval.

What happens if my registration is rejected?

Registrations are rejected by the CNMC for reasons such as:

• The sender ID does not meet format requirements (too long, disallowed characters, or purely numeric)
• No legitimate connection between the sender ID and the company could be verified
• The sender ID could cause confusion with another registered brand or public institution
• Required information was missing or inaccurate in the submission

For an SMS sender, open its details to review the rejection information. If Register again is available, correct the information and resubmit. If the message says Rejected by CNMC, contact the CNMC directly to resolve it. Klaviyo does not provide the detailed CNMC rejection reason, and its status can take time to update after you complete the CNMC requirements. Resubmissions still require review; there is no expedited path.

Contact Klaviyo Support if you need help understanding the rejection reason or preparing a corrected submission.

Frequently asked questions

Does this regulation apply to me if I'm not based in Spain? Yes. The regulation applies to all businesses sending alphanumeric SMS or RCS to Spanish phone numbers (+34), regardless of where the sending company is based. For direct registration, see the digital certificate section above. For the Klaviyo SMS form, see the authorization letter requirements.

What if I send to Spain using a short code or long code? Numeric sender IDs are outside the scope of this regulation. No action is required.

What if I have multiple sender IDs I use to send to Spain? Each sender ID must be registered separately, through either option.

Do I need to register separately for SMS and RCS? Yes. The CNMC registry covers both SMS and RCS alphanumeric sender IDs, and each channel is a separate registration — registering your SMS sender ID does not cover RCS, even if you use the same brand name. If you have already registered directly with the CNMC for SMS, follow the same process for your RCS sender ID as soon as possible. Note that the character limits differ: RCS sender IDs can be up to 40 characters, versus 11 for SMS.

Can I switch between options if one isn't working out? Yes. If you start with Option B and want more control over timing, you can pursue Option A at any point — you don't need to wait for or cancel your Klaviyo submission first.

How will I know when my registration is approved? The account owner will receive an email notification when the registration status changes. You can also check status (branded sender ID only) at any time in your Klaviyo SMS settings. For RCS senders support will contact you with any updates, including approval.

What if my legal representative doesn't respond to a direct-registration CNMC notification in time? The registration will be rejected. You will need to resubmit and go through the full process again, including the CNMC review period. Make sure your legal representative knows to expect a notification from the CNMC and responds within 10 business days.

I submitted my registration but haven't heard anything. What should I do? If you submitted via the Klaviyo intake form and have not received a confirmation, contact Klaviyo Support to verify your submission was received.

Need help?

Contact Klaviyo Support for additional guidance.

Requirements are set by Spain's CNMC and are subject to change.