Short answer: blocking a text sender works, but only on your phone and only for that specific number. The message isn't rejected by the network: it arrives, and then your phone hides it. That's effective against a sender who keeps at it (an individual, a persistent cold caller), and useless against mass spam that switches numbers with every wave. For that, you need to combine automatic filtering, STOP replies to legitimate short codes and reporting to 33700.
Updated 6 November 2026.
It's everyone's first instinct: an unwanted text arrives, you press and hold on it, look for "Block", and move on. Then the same message comes back three days later, from a different mobile number, sometimes word for word. You block it again. And again. A few months in, the blocked-numbers list has forty entries and the flow of spam hasn't budged a millimetre.
This isn't a fault in your phone: it's that blocking doesn't do what people think it does. Understanding exactly where it acts — and where it's blind — lets you pick the right tool for each type of sender, and stop fighting a stream that will never be stopped one number at a time.
Where does blocking actually act: on the network or on my phone?
On your phone, exclusively. When you block a number in Messages (iOS) or Google Messages (Android), the text is still delivered normally to your SIM card: it's the app that files it away in an invisible folder — or deletes it — before you ever see it.
That distinction has three very concrete consequences:
- The sender doesn't know they've been blocked. They get no error back, and their message counts as delivered. They'll keep writing to you without ever realising.
- Blocking doesn't follow you everywhere. It's stored in the app or in the account, not in the network. Switch messaging app, switch phone or reset the device, and depending on how the backup was made, your list can vanish.
- Blocking doesn't protect your landline, your tablet or any secondary messaging setup. If you also receive your texts on a computer through a paired app, check that the filtering is properly mirrored there.
In other words: blocking is a display filter, not a firewall. Very useful, but you need to know what you're using it against.
Who is blocking effective against?
Against a stable sender who always uses the same number. That's the most common case in real-life disputes, and it's where blocking does exactly its job.
The situations where blocking really settles the problem:
| Type of sender | Is blocking enough? | Why |
|---|---|---|
| A persistent individual (ex-partner, neighbour, online buyer) | Yes | They have only one number and aren't trying to hide it |
| A cold caller who always calls back from the same mobile number | Often | Call centres sometimes keep their lines for weeks |
| A 3xxxx/2xxxx short code that doesn't respond to STOP | Partly | Blocking hides the messages, but the subscription and the billing continue |
| A smishing campaign (fake parcel, fake bank) | No | A different number with every send, sometimes spoofed |
| A text sent through a foreign gateway | No | The displayed number is often disposable or falsified |
In the third case, be careful: hiding messages from a short code doesn't unsubscribe you from anything. If a premium-rate line shows up on your bill, you have to tackle the problem upstream — identify the service provider and demand it stop, as detailed in our guide to getting a premium-rate text charge off your bill. Blocking without unsubscribing means you keep paying without even seeing the messages.
How do I block a number properly on iPhone?
There are two possible routes, depending on whether you just want to hide messages or also cut off calls.
- Open the conversation in Messages.
- Tap the name or number at the top of the screen, then Info.
- Scroll down and choose Block this Caller.
- Confirm: the number joins the list visible under Settings → Apps → Messages → Blocked Contacts.
iOS blocking is global: it covers texts, calls and FaceTime from that number. Bear that in mind if you're blocking a business you might still want to reach by phone.
Two additional settings are worth more than a hundred blocks:
- Settings → Apps → Messages → Filter Unknown Senders: messages from numbers not in your contacts go to a separate tab, with no notification. You don't lose them, you just stop having them thrust at you.
- Report Junk: beneath a message from an unknown sender, iOS offers to report it directly. That doesn't replace 33700, but it feeds the filtering.
How do I block and filter on Android?
The principle is the same, with wording that changes depending on the manufacturer's skin (One UI on Samsung, Pixel on Google, and so on).
- In Google Messages, press and hold the conversation.
- Tap the Block icon (the no-entry sign) or the ⋮ → Block & report spam menu.
- Tick Report spam so Google can feed its detection model.
- Find the list under Google Messages → Settings → Spam and blocked conversations.
On the automatic filtering side, check Settings → Spam protection → Enable spam protection: it's that setting, not your manual blocks, that intercepts the bulk of mass campaigns. Texts classified as "spam" are filed in a separate folder you can still consult — handy when a verification code lands there by mistake.
Two details that save time:
- On Samsung, the Samsung Messages app keeps its own list (Settings → Block numbers and spam). If you have both apps installed, the lists aren't shared.
- Some manufacturers also let Android block by prefix: you can, for instance, filter everything starting with a given dialling code. Handy if the messages always come from the same foreign range — a case we cover in our article on texts from an unfamiliar country code.
Why does the spam come back after every block?
Because in an industrial-scale campaign, the number has no value. It's used for a few hours, sometimes a few minutes, then abandoned. Blocking that number is like bricking up one door in a wall that has thousands.
Three mechanisms explain this rotation:
- Disposable SIM cards and sending gateways. A spam operator uses batches of consumable numbers; blocking a single one changes nothing.
- Sender spoofing. The displayed number or name can be falsified, and sometimes matches that of a real organisation — which makes blocking not just ineffective but dangerous, since you'd risk blocking the genuine sender. We described this mechanism in the article on sender spoofing inside your bank's message thread.
- Alphanumeric sender IDs. When the message comes from a name ("INFO-LIVRAISON") rather than a number, there's often nothing to block: these headers aren't phone lines.
The practical conclusion: if you're getting fake parcel, fine or bank texts, don't waste time blocking. Forward them to 33700 (a free service run by the French carriers, see 33700.fr), then delete them. A report, unlike a block, travels up to network level and can get the source cut off — something your local block will never do.
STOP, blocking or 33700: which one for which message?
The three tools address different problems, and it's the confusion between them that leaves so many people helpless.
| Situation | The right tool | What it does |
|---|---|---|
| Marketing from a retailer you're a customer of | Reply STOP to the number given | Mandatory, free unsubscribe |
| Premium-rate subscription on your bill | STOP to the short code + written complaint | Stops the service and the billing |
| Fake text (parcel, bank, fine, tax office) | Forward to 33700 | Network-level report, source blocked |
| Commercial telephone cold calling | Registration with Bloctel | Bars cold callers from calling |
| An individual harassing you | Block + screenshot + police complaint | Cuts off contact, preserves the evidence |
The STOP reflex deserves one clarification: it's only useful if the sender is identifiable and legitimate. Replying STOP to a smishing number simply confirms that your line is live. We've set out the cases where it works and those where it makes things worse in Replying STOP to a text: does it really work?.
For harassment between individuals, the logic is completely reversed: before you block, document everything. Time-stamped screenshot, number visible, the whole message. Some people even prefer to photograph the screen with a second device to obtain evidence that can't be altered; a simple smartphone tabletop tripod is enough to get sharp, legible shots of a series of messages. Once the evidence is gathered, blocking costs you nothing.
Do I need a third-party anti-spam app?
Rarely, and never without caution. The filters built into iOS and Google Messages have one decisive advantage: they work locally or within a known contractual framework, whereas a third-party app has to access the content of your texts in order to sort them.
Before installing anything, ask yourself three questions:
- What permissions is the app asking for? Reading all your texts means reading your one-time banking codes.
- Where is the data processed? A GDPR-compliant privacy policy, with an identifiable data controller, is the bare minimum. The CNIL (French data protection authority) regularly points out that reverse directories and number databases built from users' address books are problematic.
- What do you actually gain? If you haven't turned on the native "Filter Unknown Senders" or spam protection, you haven't yet used the most effective free tools available.
In most cases, good native settings plus the 33700 habit comfortably beat any app. If the volume is such that your main number has become unusable, the real answer is structural: compartmentalise, by keeping a secondary line for sign-ups, deliveries and online shops. That's the method described in A second number for everything that isn't family and friends, and a simple dual-SIM mobile phone is often all it takes.
What if I block a legitimate sender by mistake?
It happens more often than you'd think, especially with automatic filters — a bank code, a text from the pharmacy or an appointment confirmation can end up in the spam folder.
The right moves:
- Check the folder before panicking. On iOS: the "Unknown Senders" tab in Messages. On Android: Spam and blocked conversations.
- Unblock from the list, never by asking for the message again: most one-time codes expire within minutes.
- Add the legitimate sender to your contacts. That's the best antidote to over-filtering: a number in your address book is no longer treated as unknown.
- If a code still doesn't arrive even though nothing is blocked, the problem lies elsewhere — full storage, multi-SIM messaging, network. Our full diagnostic is in Text never received: why your codes arrive late.
Think about hardware dependencies too: a full microSD card on an older Android, a portable phone charger that spares you a shutdown at the worst moment, or a document folder in which to archive the screenshots of an ongoing dispute — small details, but they matter when you have to prove something months later.
Good hygiene, in five moves
- Turn on native filtering (iOS "Filter Unknown Senders", Android "Spam protection"). That's 80% of the result, in one minute.
- Only block stable senders. Individuals and recurring cold callers, yes. Mass campaigns, no.
- Forward fake texts to 33700, then delete them. Without clicking, without replying.
- Only reply STOP to identifiable senders, and check your bill the following month.
- Keep your main number for family, friends and sensitive accounts; everything else goes through a secondary line.
To work out where a message came from before deciding what to do with it, the SMS short codes page breaks down the 3xxxx, 2xxxx and 6xxxx ranges, and the reporting to 33700 page sets out the exact procedure. If you don't yet know what kind of sender you're dealing with, start by decoding the text's sender: blocking a number you haven't identified often means bricking up the wrong door.
Frequently asked questions
Does the blocked person know they've been blocked? No. Their text shows as sent and, depending on the carrier, as delivered. No error message is returned to them. Only a complete lack of any reply might let them guess.
Can a blocked number still call me? On iPhone, no: the block covers texts, calls and FaceTime for that number. On Android, the behaviour depends on the app: Google Messages and the Phone app generally share the same list, but check both settings.
How many numbers can I block? The limit is very high and you won't reach it in normal use. The problem isn't the size of the list but its uselessness against senders who change numbers — hence the value of automatic filtering.
Does blocking stop premium-rate texts from being billed? No. Hiding messages doesn't cancel a subscription. You have to send STOP to the short code concerned, identify the service provider and, if necessary, complain in writing to both the provider and your carrier.
Should I block or report a fake bank text? Report it. Forward it to 33700, delete it, and contact your bank through a channel you already know (official app, the number on the back of your card). Blocking would be ineffective, since the displayed number is usually spoofed.
