What causes SMS messages to be delayed?

Surprisingly SMS isn’t backed by a mobile network guarantee of SMS delivery within a certain number of minutes and seconds. 

In fact the networks offer no guarantees of SMS delivery at all!

Despite this, SMS is very resilient and it’s very rare that there are network-wide issues that cause long delays to a text message being delivered.

But it does happen occasionally. 

As recently as May 2020, O2 suffered a network-wide outage with most customers being unable to make calls or send texts. The outage lasted for several hours, made national headlines and caused a major headache for millions of customers.

Thankfully these types of outages are relatively rare and most of the time we expect text messages to be delivered within seconds.

Instant SMS delivery has become more and more important as SMS is increasingly used as a way of sending secure codes for making purchases and logging onto apps and online services.

So while SMS is generally very reliable, there are occasions when a text can fail to deliver or be delayed and here we’ll be taking a look at the main reasons SMS delays can occur.

Location of the mobile phone

The precise location of the sending or receiving handset can cause a message to be delayed.

If the mobile happens to be on the border of two cell coverage areas the message can end up ‘hanging’ and not being delivered via either cell.

The issue is almost always resolved when the person moves location. This usually results in a number of messages all being delivered at the same time.

No mobile phone coverage

It’s 2022 and there are still areas of the UK where mobile coverage on some networks is patchy. I live in Bristol UK and there are still areas of the city with either very poor coverage, or even no coverage at all.

Mountains, cliffs, large buildings and other sizable obstructions will also cause dead spots in mobile coverage.

It goes without saying, no coverage, no message delivery.

When you move location and mobile coverage is resumed, messages will be delivered.

SMS delays caused by traveling at speed

You may have noticed that when you’re on the train or in a car that messages are sometimes delayed or seem to get stuck. 

We’ve seen some discussion that if you’re traveling at speeds of over 50 KPH, messages can get delayed as you speed through coverage cells although we can’t find any hard evidence for this.

Anecdotally though it does seems that traveling can cause delays to SMS delivery.

Problems with a mobile phone

Handset issues could be responsible for a number of reasons for SMS delivery problems.

Mobile phone switched off
This seems too obvious to mention but a text can’t be delivered to an inactive phone. 

SMS Inbox full
Some older feature phones have a maximum number of texts that they can receive. Deleting older text will create spare capacity for the delivery of new ones.

Text messaging blocking by the user
Most handsets will allow the user to block texts from unknown senders. You can also block texts unless they are an existing contact.

Weak battery
A weak battery can apparently cause delay to text messages being delivered. Although a number of sources are claiming this, there doesn’t appear to be any evidence for this.

Standard SMS messaging switched off
Some phones will allow you to set the default messaging app. If you use an android phone for example, you could switch the default messaging app to RCS messaging which might cause a problem if someone sends you a standard text.

Different Networks

Sending texts from one network to another almost never causes a problem, The networks are built to transfer billions of texts every day between networks.

Whenever you transfer data though, you introduce a potential area of weakness where things can go wrong in specific circumstances.

Very occasionally a data transfer error could result in an SMS delivery delay or more probably the message just won’t be delivered.

Heavy network traffic

Back in 2004, UK mobile phone networks really struggled to keep up with SMS demand. Volumes of texts were exploding and there were very regular delays in receiving texts.

It was incredibly frustrating.

But since then, the networks have massively increased their capacity and SMS volumes have now been in steep decline since 2012.  So delays caused by network traffic are very rare and would only normally be caused by huge number of people attending a large event.

This places huge numbers of people in one cell coverage so can cause bottlenecks and delays in SMS traffic.

Sending group messages

If you’ve created a group message chat thread, some people in the group can have issues with delayed messages.

In 2020 multiple T-Mobile users were reporting this issue.

The problem is that text messages are often delayed by up to 24 hours and then dumped all at once into my phone. This is looking to be a T-Mobile issue. I’m on an iPhone 11 Pro with the latest version of iOS. To sum up:

The T-Mobile community group was unable to shed any light on what the issue is caused by and it remains unresolved.

One user discovered that changing their 10 year old SIM for a new one, instantly resolved the problem, others remain scratching their heads.

Sending messages internationally

Delays when sending messages to different countries is still surprisingly common. 

Whenever texts are transmitted from one network to another internationally there is always a chance that something will be delayed. 

Mobile networks rely on global commercial and technical partnerships which add a level of complexity to message delivery.

What are the most effective fixes for solving delayed messages?

Like almost every fix for an IT issue, rebooting your phone will almost always cure delays in receiving text messages.

Have a good rummage in your phone settings. Have you disabled SMS somehow or switched off delivery from unknown contacts? Make sure you’ve haven’t inadvertently changed a message setting.

Have you recently downloaded or changed the messaging apps that you use? Can you trace the problem with delayed texts to a change in app use?

How old is the sim in your phone? If it’s ancient, try swapping it out for a new one.

If all else fails, try contacting your mobile phone provider. Don’t expect a lightning response or an instant fix but they may be able to point you in the right direction.

Understand the limitations of SMS

Occasional delays in SMS are to be expected and they will never be eliminated entirely. 

Because SMS is so dependable and instant, we’ve become conditioned to the idea that all texts should be delivered within seconds.

Sometimes that just won’t be the case and we should accept that sometimes we’ll be faced with frustrating delays.

Network reliability has improved in recent years and on the whole they provide a service that doesn’t cause any issues for almost all users.

Related articles

13 reasons why a text message does not get delivered Discover the most common reason a text message does not get delivered.

What is the maximum length of an SMS text message? How long can text messages be and does it cost more to send a longer message?

6 reasons why people are unsubscribing from your SMS list Find out how not to annoy your customers with SMS so that they want to get off your list ASAP.