What's changing?

Spain's national telecom regulator, the CNMC (Comisión Nacional de los Mercados y la Competencia), now requires all alphanumeric sender IDs to be registered in a national Alias Registry.

Starting September 15, 2026, Spanish mobile operators will block any SMS sent using an unregistered alphanumeric sender ID. If your alphanumeric sender ID isn't registered by that date, your messages won't be delivered.

Key terms

Before diving in, here are some terms you'll see throughout this process:

Required Information to Register your Sender ID

Regardless of your registration path, you'll need to provide:

Sender Information:

• The sender ID (alias) you want to register
• How the sender ID connects to your business (legitimate linkage type)

Business Information:

• Business type: Individual (PF) or company (PJ). 
• Tax identification number (NIF for Spanish entities, EU VAT ID, or equivalent)
• Registered business name

Legal Representative Information:

• Full name (first name, surname)
• ID number (NIF, passport, or equivalent)
• Email address (this is where CNMC sends verification notifications)

Third Party (Tercero) Information:

• If an entity other than your company and Twilio is involved in managing or sending messages with your sender ID (e.g., a marketing platform or agency), their details are required.

Sender ID format requirements

Your sender ID must comply with these CNMC specifications:

• Length: 3–11 characters
• Allowed characters: Letters (a–z, A–Z, including ñ and ç), numbers (0–9), and special characters: @ & - _ . + and spaces

Prohibited:

• Purely numeric sender IDs
• Generic terms that don't identify a specific business (e.g., "Message", "Bank", "Alert")
• Leading or trailing spaces
• Consecutive spaces
• Accented vowels (á, é, í, ó, ú)
• Offensive or misleading content

Important: Sender IDs are case-sensitive. "BRAND" and "Brand" are treated as distinct aliases and each requires separate registration.

Twilio Supported Registration Paths

Twilio supports two ways to get your sender ID registered with the CNMC:

How to choose your path

Choose Self Registration if:

• You already have a Spanish FNMT digital certificate or an eIDAS-qualified EU certificate
• You want direct control over your CNMC submission
• You want fastest path to register

Choose Twilio as Authorized Representative if:

• You don't have and can't easily obtain a qualifying digital certificate
• You're a company outside Spain/EU without local representation

Path #1: Self-Register your Sender ID with CNMC 

Here's the end-to-end process for Self Registration:

1. Go to the CNMC Alias Registry portal
   Visit https://tramites.cnmc.gob.es/formulario/213/ and authenticate with your digital certificate.
2. Complete the Alias Registration Form
   Fill in your company details, legal representative information, and the sender ID you want to register. When completing the form:

• Select Twilio as your PRO (Provider)
• If an ISV or other platform sends traffic on your behalf using this sender ID, list them as a Third Party (TERCERO)

Important: You must choose Twilio as the PRO in order for traffic to be delivered by Twilio. 

3. Submit your Registration
   Review your information and submit. The CNMC will issue a justificante (proof of submission PDF). Download and save this document with Twilio.
4. Your Legal Rep Authorizes the Registration 
   The CNMC will send an email to your legal representative. The representative must log into the portal with their digital certificate and approve the registration within 10 business days. If you miss this window, your registration is rejected and you'll need to resubmit.
5. Submit your proof of registration to Twilio
   Log in to the Twilio Console and navigate to Numbers and Senders to create a new Spain Alphanumeric Sender ID registration. Complete the registration for while also providing the proof of submission from the CNMC portal. If you need the alphanumeric sender ID in many accounts, you can also specify additional accounts to add to your registration.
6. Twilio Provisions the Sender ID
   Once your application is approved by Twilio Ops and your registration on the CNMC is approved, you will have an alphanumeric sender ID provisioned to your account. If Twilio has approved your registration but we are still waiting on approval in the CNMC, then your registration will show as in review as it is pending regulatory approval. 

Path #2: Twilio as Legal Rep (coming soon)

Only companies outside of Spain can use this registration flow. 

Here's the end-to-end process for Twilio as Legal Rep:

1. Confirm Eligibility 
   Only non Spanish entities can utilize the Twilio as Legal Rep flow. If you are an ISV and need to register your end user, you will need to first sign a supplemental agreement with Twilio prior to registering. Please contact your account executive to receive the agreement. 
2. Complete the Console Form 
   Log in to the Twilio Console and navigate to Numbers and Senders to create a new Spain Alphanumeric Sender ID registration. Choose the path for using Twilio as Lega Rep. Complete the registration form. If you need the alphanumeric sender ID in many accounts, you can also specify additional accounts to add to your registration.

During this process, the following documents will be required:

• Proof of Business: Business document showing legal name, address, registration number, and officers of company
• Proof of Authorized Representative: Government ID of the officer listed on the business registration documents
• CNMC Letter of Authorization for Foreign Entities: The CNMC LoA must be signed by the legal representative of the Sender ID holder
• Proof of Sender Link: Proof that the business has the right to use the specific Sender ID requested  if the sender ID is not the business name. 

3. Twilio Review
   The Twilio operations team will review your application. If the Twilio operations team approves the application, we will then submit your information to the CNMC
4. CNMC Review
   The CNMC will review your application. Twilio will be the legal representative to the CNMC for your sender ID. Once approved, Twilio will provision your sender ID.
5. Twilio Provisions the Sender ID
   Once your application is approved by Twilio Ops and your registration on the CNMC is approved, then your alphanumeric sender ID will be provisioned to your accounts.

Frequently asked questions

Do I need to register each sender ID separately?

Yes. Each unique alias requires its own registration with the CNMC. All alphanumeric sender IDs are case sensitive. 

What happens if I don't register before September 15, 2026?

Your messages using unregistered alphanumeric sender IDs will be blocked by Spanish carriers. They will not be delivered.

Can I keep sending while my registration is being reviewed?

During the testing phase (before September 15, 2026), yes. After enforcement begins, only registered aliases will be delivered.

I'm an ISV with many customers using sender IDs. What should I do?

Each sender ID used by your customers must be registered. All of your customers with digital certificates should Self Register and list you as the Third Party. Be sure to share your exact company name and Tax ID with the customer as an exact match is required for traffic to not be blocked. Once your customer has registered, submit this information to Twilio via the Console. 

How much does registration cost?

Registration with the CNMC is free. There is no charge from the CNMC for registering or maintaining a sender ID.

What if my registration is rejected by the CNMC?

In the self registration flow, the CNMC will notify you of the reason. You'll have 10 business days to submit corrections. 

I don't have a Spanish digital certificate. What are my options?

You can either: (1) obtain an eIDAS-qualified certificate from a qualifying EU country, (2) appoint a representative who holds a valid certificate to submit on your behalf, or (3) use Twilio as the legal representative.