To send SMS to Spanish numbers (+34) with a brand name as the sender, you must register that alphanumeric sender ID, which Spain calls an alias, in the CNMC’s Registro de Alias and name the messaging provider allowed to send it. Since 15 September 2026, operators and aggregators must block SMS, MMS and RCS messages whose alias is not registered, or that arrive through a provider the alias owner has not enabled.
This guide explains the rules in Order TDF/149/2025 and CNMC Circular 1/2026, which aliases the registry accepts, and how to register. If you send bulk SMS to Spain, start with the audit in step one below.
What is the CNMC Alias Registry?
The Registro de Alias is a database run by the Comisión Nacional de los Mercados y la Competencia (CNMC), Spain’s competition and telecoms regulator. It records every alias approved for messages to Spanish numbers, who owns it, and which providers may send traffic with it.
It rests on four official texts:
- Order TDF/149/2025 of 12 February 2025, the government’s measures against spoofed calls and texts. Article 8 requires companies and public bodies to register aliases before use and requires providers to block unregistered ones.
- CNMC Circular 1/2026 of 18 March 2026, published in the BOE on 27 March 2026, which sets the procedure, the format rules and the obligations of each provider.
- CNMC Circular 2/2026 of 5 June 2026, which lets owners act through a representative appointed by signed letter and makes bulk uploads by providers a permanent option.
- Order TDF/558/2026 of 4 June 2026, which moved the start of blocking from 7 June to 15 September 2026 so that registrations could be completed.
On 1 September 2026 the CNMC urged companies to finish registering and to answer any CNMC notifications before that date. The Circular also cites the CEPT’s October 2025 recommendation ECC/REC/(25)04, which encourages national alias registries and blocking of unregistered senders across Europe. For other markets, see our guide to SMS sender ID rules by country.
Which senders and messages are covered?
The Order defines an alias as an alphanumeric string in the sender field of an SMS, MMS or RCS message that identifies the sender but cannot receive a reply. The rules cover:
- Every alias in A2P messages to Spanish numbers, whether used for one-time passwords, alerts or marketing.
- Spanish and foreign companies alike. A business based outside Spain that texts customers with Spanish numbers must register its aliases too.
- Public administrations that send with an alias.
- Every provider in the chain. Mobile operators, full MVNOs, aggregators and resellers able to block traffic must be listed in Spain’s Registro de Operadores and registered in the alias registry as registered providers.
Two things are outside the scope of the Circular:
- Purely numeric senders from the Spanish numbering plan, the SMS short-number ranges or the international E.164 plan.
- Messages to non-Spanish numbers, including foreign subscribers roaming in Spain.
Numeric senders have a separate restriction. Since June 2025, article 7.1 of the Order has required operators to block messages arriving from abroad over an international interconnection that show a Spanish phone number as the sender, unless the recipient is roaming. A Spanish long code is therefore not an automatic workaround for traffic that enters Spain from another country.
What does a valid alias look like?
Annex III of Circular 1/2026 sets the format for SMS and MMS aliases:
| Rule | Requirement |
|---|---|
| Length | 3 to 11 characters |
| Allowed characters | a-z, A-Z, ñ, Ñ, ç, Ç, 0-9, single spaces, and @ & – _ . + |
| Not allowed | Accented letters; leading, trailing or double spaces; ! # % ( ) * , / : ; < > = ? € and similar symbols |
| Numbers only | Not accepted as an alias |
| Generic words | Rejected if they do not identify the sender, for example “Banco”, “Urgente” or “Vuelo” |
| Place or personal names | Only if tied to the owner: “AytoMadrid” is acceptable, “Madrid” is not |
| Changes after registration | Not permitted; altered forms such as a different capitalisation must be blocked |
The practical consequence of the last rule: send the alias exactly as registered, character for character.
Each alias also needs a legitimate link to its owner: a trademark registered with the OEPM or EUIPO, a trade name registered with the OEPM, the company name in the Registro Mercantil, an internet domain, or a name in another national or international public register. An owner with none of these can declare that it uses the alias legitimately and habitually in its business. If two owners claim the same alias, a matching trademark or trade name wins, then a matching domain, then the company name, and otherwise whoever applied first.
What happens to messages that don’t comply?
Since 15 September 2026, registered providers must block, depending on their role in the chain:
- messages with an alias that is not in the registry;
- messages with a registered alias sent through an originating provider the owner has not enabled, or not sent by a third party the owner has authorised;
- messages with a registered alias received from a provider that is not itself registered;
- messages with a foreign company’s unregistered alias arriving over an international interconnection. If the recipient is a Spanish subscriber roaming abroad, the operator delivers the message but replaces the sender with “NO VALIDADO”.
Blocked messages are simply not delivered. The CNMC notes that companies can still reach customers without the alias, and that missing or new aliases can be registered at any time after the deadline. Registered aliases are also suspended automatically after 12 months without use and cancelled if they are not reactivated within a month.
Who can submit the registration?
- The alias owner (titular): the company or public body that uses the alias.
- The originating provider (proveedor de origen, or PRO): the first registered provider the owner enables to send with the alias, acting on the owner’s behalf.
- An authorised third party (tercero): for example a CRM or SaaS platform with an SMS channel, a marketing agency, a group company or a franchise.
When anyone other than the owner files, the application stays “pending authorisation” until the owner approves it, and the owner has 10 working days to do so. Whoever acts in the registry needs a digital certificate valid for dealing with Spanish public administrations. Owners can appoint a representative with a signed authorisation letter on the CNMC’s model, which is available in English for foreign companies. Originating providers can bulk-upload applications covering at least 20 owners or 50 aliases.
How do I register an alias, step by step?
- Audit every sender ID you use for Spain. Pull the alphanumeric senders from your platform logs for +34 traffic, including department, campaign and test aliases, and note the exact capitalisation of each.
- Check each alias against the format rules. Rename anything generic, accented, too long or purely numeric before you apply, because a registered alias cannot be edited.
- Document the legitimate link. Match each alias to a trademark, trade name, company name or domain you own, and keep the evidence on file, such as a trademark certificate, a company register extract or your registrar’s record for the domain. You will sign a responsible declaration (declaración responsable) that you hold the right, and the CNMC can ask for the evidence at any time.
- Decide who files. File yourself, let your originating provider file, or appoint a representative by authorisation letter. Whoever files needs a digital certificate valid in Spain.
- Collect the application data. The form asks for the alias, the type of link, the owner’s legal name, a Spanish NIF or EU VAT number, the registered address, representative details, an activation date, an optional end date, and one or more originating providers chosen from the registry’s list.
- Submit through the CNMC electronic office. The CNMC’s registration guide walks through each screen. If someone filed for you, approve within 10 working days. If the CNMC asks for corrections, you have 10 working days to respond.
- Wait for review. The CNMC has up to one month for an individual application and three months for a bulk upload. The alias can be used from the day after it is registered.
- Verify and maintain. Check the alias on the CNMC’s public registry lookup and keep the record current. Add or remove providers when you change suppliers: if your only originating provider leaves, you have one month to enable a new one before the alias is cancelled, and a cancelled alias cannot be taken by anyone else for six months.
How SMS.to helps with Spanish sender registration
Registration is half the job. The other half is making sure your traffic reaches Spanish networks through registered providers, with the alias exactly as recorded. When you send SMS to Spain with SMS.to, we:
- review the sender IDs on your account against the CNMC format rules and flag any that need renaming;
- tell you which provider details to enter in your application;
- can guide you through registration or submit it on your behalf where you authorise us;
- return a delivery report for every message through webhooks, so blocked traffic shows up straight away instead of as silent failures;
- advise on numeric sender options for traffic that does not need a brand name.
For login and payment codes, keep the alias short and registered, and plan a retry or fallback for users whose code does not arrive; our guide to OTP best practices covers timing and retries. Registration does not replace consent for marketing messages; see SMS marketing compliance and automated opt-outs.
Rules change often. This guide reflects the rules as of September 2026; check with your account manager before launching a campaign.
FAQs
Is registering an alias free?
The CNMC’s procedure page lists no fee, and Circular 1/2026 puts the cost of setting up and running the registry on the CNMC. Messaging providers pay to adapt their own systems.
My company is not in Spain. Do I need to register?
Yes, if you send messages with an alias to Spanish numbers. The Circular requires foreign companies to register their aliases, and messages from a foreign company’s unregistered alias are blocked unless the recipient is roaming abroad.
Can I keep sending while my application is pending?
Not with the alias. An alias can only be used from the day after the CNMC registers it. Until then you can reach customers without the alias, for example from a numeric sender, as the CNMC itself points out.
Does the registry cover RCS as well as SMS?
Yes. It covers SMS, MMS and RCS. RCS aliases follow GSMA format guidelines and must clearly identify the owner’s brand, trade name, company name or domain.
What if someone else has registered my brand name?
You can ask the CNMC to decide who has the right to use it. A registered trademark or trade name takes priority, then a matching domain, then the company name, and otherwise the first application.
Sending to Spain under several brands, or moving Spanish traffic from another provider? Talk to sales and we will review your aliases and set up your Spanish traffic before your next campaign.
