Mobile phone in hand

13 reasons a text message does not get delivered

No SMS campaign ever achieves a 100% delivered rate. There are just too many variables that will always cause a small percentages of message failures.

What are the main reasons for text message non-delivery? (We have a separate article that runs through the main reasons for text message delays.)

Every text message that goes through our platform generates a delivery report. But sometimes these don’t provide the precise reasons for SMS failure.

This short article runs through the top 13 reasons a message might fail to arrive on the recipient’s phone.

1. You’ve got an invalid mobile number

Whenever a human gets involved in data collection, there is bound to be the occasional error. 

One of the most common reasons for non-delivery is simply that the mobile number (also known as an MSISDN) is incorrect. Either the customer gave you the wrong number or you entered it incorrectly into the database.

It’s also possible that the mobile number has been discontinued, so the number used to be correct but is no longer active on the network.

A common error is to attempt to send a text to a landline. Unless the recipient has this service switched on, then the message will not arrive.

Either way, if the number’s wrong, the SMS will fail.

2. The phone is switched off

Blue retro mobile phone

This would seem unlikely as we’re all glued to our phones for hours every day but some folk do keep their phones switched off for extended periods.

The message will expire after about 48 hours, so if a phone is switched for a couple of days, it will never arrive.

3. The mobile phone is roaming in a different country

Union flag

Most mobile contracts allow all services to work abroad but there are a few contracts that do not permit receiving texts outside your country.

When this is the case and a person is roaming, then a message won’t be received.

4. The user may have blocked or filtered SMS from your sender ID

Blocked text messages

Most mobile handsets allow you to block messages from any numbers.

This typically can’t be set if you are using an alphanumeric sender ID but could cause non-delivery if you have set the sender ID as a reply number.

Iphone users also have the ability to filter unknown senders into a separate list. Notification alerts will also be switched off.

So if messages are being filtered, then texts will arrive but the user might not be aware of them.

5. Your sender ID is not permitted in the country or network that you’re sending to

The SMS Works Padlock

Some countries do not permit dynamic, alphanumeric sender IDs. If you send a text to a contact in a country with restricted sender ID regulations, then your message will probably not arrive.

Some networks simply automatically switch the sender ID to a random number to allow delivery, others will simply block the text.

Countries and individual networks frequently change their policy on this, so if possible, always test in advance.

6. SMS Message delivery may be subject to time restrictions

In order to avoid consumers being bombarded by marketing texts at anti-social hours, some countries impose restrictions on when marketing texts with alphanumeric sender ID can be sent.

For example, in France, you are only permitted to sender marketing texts between 0800 and 2000. 

Marketing texts sent outside these hours will be blocked.

7Network filters and anti-spam blockers

Increasingly, networks are implementing anti-spam and phishing filters in an attempt to prevent rising spam problems in some countries.

If your message looks like spam or could be interpreted as a phishing attempt then some networks will automatically block the text.

Occasionally this means that legitimate traffic containing certain keywords may get blocked.

8. The message contains non-permitted characters

Most companies use the GSM characterset to send SMS messages. If your text contains odd characters outside the standard, then your message will be rejected by the network.

To allow for the sending of emoticons, messages can be sent using UTF-16 encoding, although this hugely reduces the number of characters per text to just 70.

This unicode character detector helps you identify any non-standard characters.

9. Customer is subscribed to a Do Not Disturb (DND) service

Some networks operate a ‘Do Not Disturb’ service which allows users to opt out of receiving any marketing texts.

Subscribers will therefore not receive SMS messages if this option is available and activated.

10. Network issues

From time to time, networks suffer from data and text outages. These days, this is relatively rare.

But as recently as June 202, T-Mobile suffered a massive outage for 12 hours affecting SMS messages and voice services.

Down detector showing network outages
Source Openstreet

11. SMS message is too long

Most networks have a maximum message length of around 1600 characters although this does vary. Messages that are over 160 characters long will be split and sent as concatenated texts

If your message exceeds the number of characters permitted, the SMS will be rejected.

12. Mobile service suspended

If a customer fails to pay their monthly mobile phone bill, then the mobile network will switch off the customer account and no messages will be delivered!

13. Mobile phone memory exceeded

This one is pretty rare. If someone is still using an old feature phone with limited capacity, then if the SMS message box is full, then no further messages can be received.