Guides

13 minutes to read

Sep 23 2026

Sender ID Registration in the EU and UK: Why Your SMS Gets Filtered

Victoria Thomson

Your delivery report says 96% sent. Your conversion data says the campaign barely moved. The usual reaction is to blame the copy, the timing or the offer. In our experience, the campaign is rarely the problem. In many European markets the messages never reached the handset, because the sender name on them was never registered with the operator.

Sender ID registration is the process of declaring your alphanumeric sender ID — the "ACME" a subscriber sees instead of a phone number — to a mobile operator or a national registry before you send traffic. Where it is required and skipped, operator filters rarely reject the message loudly. They rewrite it, delay it or drop it quietly, and your dashboard still counts it as sent.

This guide explains how that filtering works, what registration actually changes, and why the sender ID registration rules differ in every EU and UK market you send to. It ends with a country-by-country table of requirements as they stand on the day of publication.

Why unregistered senders get filtered instead of rejected

Every operator runs an SMS firewall between the interconnect and its subscribers. The firewall scores each incoming A2P message on route origin, content pattern, volume and — increasingly — on whether the sender name is known. Without sender ID registration, an alphanumeric sender that no one has declared looks exactly like a brand-impersonation attempt, because that is how most smishing traffic arrives.

Operators have a strong reason to be strict. In the UK alone, four in ten mobile users reported receiving at least one suspicious message in the previous three months (Ofcom, 2026), and mobile providers already block an estimated 600 million plus scam messages a year (Ofcom, 2026). A filter tuned to catch that volume does not give an unknown sender the benefit of the doubt.

What the filter does with your message depends on the market. Some networks overwrite the sender with a generic name such as "Info" or a random numeric code, so the customer receives a text from nobody they recognise. Others route it through a low-priority queue, and the OTP arrives after the login page has timed out. The worst case is a silent drop: the message is accepted at the SMSC, a "submitted" status comes back, and nothing reaches the phone. At BSG, we've seen that teams who only track the submitted count never notice this — the gap appears only when you compare handset-level DLR against what was sent.

What sender ID registration changes — and what it doesn't

Registration turns your sender name from an unknown string into a verified identity tied to a legal entity, a use case and, in most markets, sample content. Once the operator has that record, the firewall can match the incoming message against it instead of guessing. The practical effect is higher operator trust and, with it, higher and more stable deliverability on the routes where you are registered.

Sender ID registration is not a guarantee. A registered sender still has to respect opt-in rules, local sending hours and content restrictions, and the operator keeps the right to block a sender whose traffic drifts away from the declared use case. Registration removes the identity problem; it does not exempt anyone from anti-spam policy, and any provider who promises "100% delivery" after registration is describing something that does not exist in A2P messaging.

The contrast is still stark. Based on what we observe across the bulk SMS campaigns we support into Central and Eastern Europe, an unregistered brand sender on a registration-required network typically arrives as a generic name or not at all. The same traffic on the same route delivers as intended once the sender is on the operator's list. Nothing about the message changed. What changed is that the operator now knows who is sending it.

Every EU and UK market registers senders differently

This is the part most teams miss. There is no single European rule for sender ID registration, and the requirements in one member state say nothing about the neighbour. In our experience working with e-commerce and fintech clients in the region, the markets fall into four patterns.

The first group runs an open, dynamic sender ID model: Germany, the Netherlands, the Nordics and the Baltics accept an alphanumeric sender without pre-registration, and the firewall judges the traffic on reputation and content instead. The second group registers senders per operator, with paperwork and fees — Romania, Bulgaria, the Czech Republic, Croatia and Slovenia all fall here, and each operator inside the country can have its own price and lead time.

The third group restricts alphanumeric branding altogether. Hungary and Malta overwrite every sender with a numeric one. Italy allows a branded sender only to companies that hold Italian VAT and PEC and have registered the name in the AGCOM database through a licensed Italian provider; everyone else is delivered with a local numeric sender. The fourth group, which is really just the UK, requires no pre-registration but filters hard on identity. International numeric senders, non-UK short codes, generic names such as "Alert" or "Verify" and senders with special characters are blocked outright. Promotional content has to be whitelisted with the sender, text and links before it goes out.

A client scenario shows why the pattern matters. A European fashion retailer we work with launched the same promo, with the same alphanumeric sender, into six markets. In Germany and Poland it delivered as expected. In Hungary customers saw a numeric sender and ignored the text. In Italy, where the company had no local entity, the branded name was replaced by a local number. In the UK the campaign stalled until the sender and copy were whitelisted. Same campaign, same route, four different outcomes — and none of them caused by the creative.

Sender ID registration requirements by country: EU and UK

The table below summarises what each EU member state and the UK require from an international A2P sender, based on BSG routing data as of September 2026. "No pre-registration" means the operators accept a dynamic alphanumeric sender for international traffic; it does not mean the traffic is unfiltered. Fees are operator-level and quoted without margin or tax; treat them as an order of magnitude and confirm before budgeting.

Two things stand out in the table. First, "no pre-registration" markets are the majority, which is exactly why teams assume Europe is easy — until one campaign hits Bulgaria or Italy. Second, the markets that do require sender ID registration rarely agree on what a sender needs to prove: Slovenia wants a local registration number, Romania wants a stamped contract, the Czech operators want an authorization letter for finance and e-commerce brands. The wider country-level rules on content, sending hours and opt-in are collected on our SMS features and regulations page.

How to register your sender ID correctly for each destination

The mistake we see most often is registering once, in the home market, and assuming the sender travels. It does not. Sender ID registration is per country and, in most of the markets above, per operator, so the work has to start from a list of destinations rather than from a list of senders. For the businesses we work with in the EU, the following sequence avoids the usual rework.

1. Map every destination and split it by pattern: open, registration per operator, alphanumeric restricted, whitelist-driven.
2. Classify traffic as transactional or promotional and, where the operator distinguishes them, use separate sender IDs for each — a promo sender that also carries OTPs gets both blocked when the promo copy trips a filter.
3. Check identity rules before choosing a name: no generic words, no special characters, a name that matches the legal entity, brand or product.
4. Assemble one document pack per country: company name and website, registration number, sample content per use case, traffic type, and a signed Letter of Authorization where the operator or aggregator asks for one.
5. Budget fees and lead times per operator, from same-day in Slovenia to a couple of weeks where a stamped contract has to travel.
6. Test each registered route with handset-level delivery reports before the first campaign, so a rewrite or a silent drop is caught on a test number and not on the customer base.

Step six is where registration pays for itself. What our clients have found is that a short pre-launch test on a dedicated SMS testing system shows how the sender actually renders on each network: branded, generic or numeric. That is the only way to confirm the paperwork did what it was supposed to do. Compliance on the content side, from opt-in to sending hours, is covered separately in our guide to SMS marketing compliance.

Ready to check your sender setup?

If you are sending into more than two European markets with one sender name, there is a good chance part of your traffic is being rewritten or filtered without you seeing it. Our team can go through your destination list, tell you which operators need sender ID registration, which documents each one asks for and how the name currently renders on each route. Talk to the BSG team for a setup review — we have done this for the same markets before.