When SMS don’t arrive – reasons and guidelines

The most common reasons for SMS that are not being delivered

You have planned and created your first SMS campaign and the moment has come: You click “Send.” However, a later look at the status reports frustrates you: some SMS have not reached the recipients. Clearly, you’re annoyed. The good news is: In many cases, it is avoidable that SMS do not reach the recipients. To make this happen, you just need to be well informed about your recipients in advance. In this blog post, we would like to give you an overview of the most common reasons for SMS that do not arrive.

End device does not respond

It happens again and again that the reason for the lack of delivery lies with the receiving device. In some models, there are occasional problems with the GSM module that receives the SMS. In those devices, this module stops working and is only able to receive SMS agin after a restart. This means that to fix this problem it is necessary to restart the phone. Of course, we are aware that this may be out of your control, but unfortunately this is also one of the most common reasons why your SMS may not deliver.

Problems with the network provider

It is also possible that the lack of delivery is due to problems with the network provider. Unfortunately, we cannot explain the possible constellations here; they are part of the carriers’ complex systems. However, you have certainly experienced such a situation before, for example on New Year’s Eve, when there is such a high volume of messages that SMS only reach their recipients hours later. However, most often a simple technical malfunction is the result of a problem at the network provider. Furthermore, it is also possible that a network provider rejects your message. This is usually because the network provider’s filters are filtering your message. This happens most often when international SMS are sent when the sender has not acquired sufficient information about international regulations beforehand.

A few words on international regulations

Unfortunately, the international SMS market is very inconsistent and difficult to keep track of. Almost every country in the world has its own rules that decide what is allowed and what is not. Not even the EU countries have uniform regulations. Therefore, it is absolutely necessary that you thoroughly inform yourself about the regulations of the recipient country in advance, no matter where you are sending SMS. In addition to the permitted content, you also need find out about opt-out regulations. In some countries, you can expect heavy fines if you do not comply with the rules. Going beyond the specifics mentioned below, you should also pay attention to the time at which you can send SMS. If you send an SMS outside of the permitted timeframe, the message is usually cached and delivered later.

We recommend our blog post “International communication – These country-specific rules you must observe in your SMS campaign”. It contains a table where you can get a first overview of the respective regulations. Nevertheless, please inform yourself separately about your individual recipient countries.

The following points are the most common reasons why SMS do not reach your, mostly international, recipients. Please note that we cannot prevent the filtering of the network operators. Furthermore, we cannot see why an SMS was rejected by the respective carrier. However, the reasons explained in this article should give you an idea of what to look out for in order to make sure your message is being delivered.

Good to know

Not all foreign carriers support 2-way messaging with international numbers. Be sure to check this as well if you want to receive replies from your recipients.

Content of the SMS has been filtered

Carriers have filters where your SMS can get “stuck”. Here, it can happen that your SMS does not arrive because it does not meet the national guidelines and the carrier therefore filters it. Different content is prohibited in different recipient countries, for example messages dealing with gambling or cosmetics. It may also be necessary to have your content registered or approved in your recipient country. Not least because of this, it is of great important that you educate yourself in advance about the regulations of the recipient country. In a few countries it is also forbidden to send URLs in SMS.

Sender ID

Sender IDs can also become a problem in international SMS sending. The sender ID is the sender name that is sent along with the message. By sending via SMS gateway providers you usually have the option to send alphanumeric sender names along. This has the advantage that your recipients immediately know who is writing to them, even though they do not know your number.

In some countries alphanumeric senders are not supported, in others certain numbers are converted. Especially when using alphanumeric senders, it can therefore happen that your SMS does not reach its international destination. Here too, however, you need to find out about the national conditions in advance, because many countries accept foreign numeric senders, but a few do not. You should also find out whether you have to register as a sender in the recipient country in advance. If this is the case, some carriers may also refuse to allow you to send SMS.

How can you avoid that your SMS do not arrive?


When you send an SMS, the message can be sent using different encodings. You probably already know the standard encoding GSM 03.38. It allows you to send 160 characters in a single SMS. However, certain characters are not covered by the GSM alphabet. For example, if you use only one Arabic, Cyrillic or Hebrew character, the encoding of the message changes to Unicode and you only have 70 characters at your disposal. Emojis are also encoded in Unicode. In other countries, this can cause problems because a few carriers cannot handle Unicode messages. Thus, your messages may not be delivered due to the encoding. What is more, not only the type of characters is important in international SMS sending, but also the number of allowed characters varies.


Most of us are used to SMS messages containing up to 160 characters. However, as you saw in the previous section, this is only the case under certain conditions. Unfortunately, correct coding is not the end of the story: other countries also allow different SMS lengths. In China, for example, a GSM-encoded SMS may only contain 130 characters, while a Unicode message may only contain 65 characters. In addition, certain carriers in other countries may not process concatenated SMS. This means that sending overlong SMS messages that exceed the maximum number of characters of a single SMS will not work there.


As mentioned above, some countries require you to register or unlock certain aspects of your messages in advance. This doesn’t just apply to content and sender: you may need to submit a form to network operators in advance, registering your company to send SMS. If you do not do this, your SMS dispatch will fail in most cases. Again, we can only advise you to do thorough research, because messages sent without permission may result in fines.

Your message has been blocked

If you do not adhere to certain specifications, you may also be blocked by certain carriers for the recipient number in question. This blocking can last a few hours, depending on the country and carrier, or it can happen permanently. Especially if you send multiple messages to the same number in a short period of time, you will most likely be blocked. In some countries it may even happen that your SMS is not delivered because the recipient has already received too many SMS that day, no matter from which sender.

SMS that fail to arrive – an annoyance that can be avoided

These are the most common reasons for SMS not reaching their destination. Of course, other incidents can also occur that cause an SMS not to be delivered, but this is the case far less often. If you have the impression that your SMS does not arrive at one of your recipients for other reasons, please do not hesitate and contact our support. Tell us the message ID or the recipient number and the time when the message was sent and we will find out why your SMS did not arrive as soon as possible. In our helpdesk article “SMS has not been received” you can also find tips on how to proceed with the status report “Not delivered” as well as information on how to make a complaint to get a refund.

Best wishes
Your sms77 team

Header: iStock.com/Makhbubakhon Ismatova

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