SMS not sending? 10 reasons and how to fix them

Business owners and marketing managers use SMS because it offers higher engagement and open and click-through rates than any other marketing channel. It’s understandably one of the most popular and powerful messaging platforms there is, but it’s not simply a case of hitting ‘send’ and hoping for the best.

1. Invalid numbers

This is the single most common reason for SMS delivery failure. Just like an error in an email address, a text message cannot be delivered to an incorrect number. 

A wrong number can be the result of an incorrect number being supplied by a customer, or could be a simple error in your database entry. Another reason for an invalid number notification would be attempting to send an SMS to a landline rather than mobile number. 

If your contact list has more than its fair share of invalid or deactivated numbers, it may signal to carriers that you have an outdated list, or that recipients are no longer interested in receiving your messages, so it’s important to keep your data up to date.

 2. Incorrectly formatted numbers

Mobile numbers need to be correctly formatted in order for messages to be delivered. Check for example that when you’re sending a message to phones registered in a different country that you use the correct country code and number format. Forgetting to include a prefix can also result in a failed delivery – for example, all messages being sent within the US, must begin with the country prefix ‘1.’ 

3. Using the wrong messaging type

If you’re trying to send SMS messages from a personal phone number, you’re using a peer-to-peer (P2P) protocol which is reserved for messaging from one individual to another – for example when you message a friend or family member.

Application-to-person messages (A2P) is used by businesses. This requires that the sender be registered with an SMS application before they can send SMS in volume. If you are in the business of sending large amounts of SMS on a regular basis and you want to send in the most cost-effective and efficient way possible, you could begin by exploring a toll-free, short code or 10DLC option.

4. The recipient has opted out

There are best practice rules and procedures that businesses need to adhere to when it comes to sending SMS. One of the most important involves consent. Just as consumers can choose to opt-in to receive news and notifications from a business, they can also choose to opt-out at any time. If you are sending text messages to someone who has decided to opt out, your messages will not be delivered.

 Read our SMS Marketing guide to learn more. 

5. Network issues and filters

In some cases, there’s no error on your part and the failure to send lies with the carrier. There’s lots of reasons for this, including congestion or network issues. If your carrier is having problems with their systems, look out for updates online regarding outages or repairs from your carrier, and restrict your SMS message activity while this is happening. Sometimes even the way a message is constructed and worded can lead to a perfectly genuine message being blocked by network filters which differ from carrier to carrier. These filters are designed to reduce the incidence of spam and phishing but can occasionally trap legitimate messages containing certain keywords too. 

6. Shortened links and illegal content

A link in your message can also cause a problem, particularly if they’ve been shortened by a third-party app. Alarm bells can ring because link shorteners are often used to disguise phishing links so consider whether you need to add a link to your message at all. If you do need one, opt for a longer link with relevant text to reduce your chances of being blocked.

The Cellular Telecommunications and Internet Association (CTIA) — a regulatory body that enforces guidelines for SMS messages — prohibits messages with any SHAFT content i.e. content relating to sex, hate speech, alcohol, firearms, and tobacco. Text messages containing such content will automatically be blocked by the receiving carrier. If your business sells alcohol, you can send SMS campaigns in certain circumstances, providing you have the necessary age verification protocols in place.

 7. The recipient has activated Do Not Disturb (DND)

Some recipients can activate a Do Not Disturb mode on their phone, which will cause incoming messages and notifications to be silenced. This creates uncertainty for senders, as they may assume messages are undelivered when they’ve been successfully sent but haven’t been opened or read. If your message is an important one about a delivery update or an extreme weather alert this creates a problem. One way to reduce the likelihood of this happening is to remind customers to add you to their ‘allowed’ list.

 8. Conflicting SMS applications

This is a problem that cannot be solved from the sender’s side, as it’s down to the recipient to adjust their device settings. Sometimes, multiple applications on a recipient’s device can receive SMS messages. These different applications can fight to receive the same message which can result in conflict and the message not being delivered at all.

As a sender it’s wise to review your send lists frequently so that you’re not sending to any phone number that is consistently having trouble receiving SMS or MMS messages.

 9. Delivery and time restrictions

In order to prevent consumers from being bombarded by marketing texts at anti-social hours, many countries impose restrictions on when marketing texts can be sent. Messages sent outside of these hours will automatically be blocked. The TCPA rules prohibit sending text messages anytime after 9pm and before 8am in a recipient’s time zone, but certain states have more restrictive rules, for example Florida which prohibits texts between 8pm and 8am.

10. Message length

Some networks impose restrictions on the length of text messages to optimize network efficiency.  When a sender attempts to transmit a message that exceeds these limitations, the message may be automatically broken into multiple parts, or in some cases, it may fail to send altogether.

This limitation can pose challenges to users who need to convey detailed content, as the fragmented messages may reduce communication clarity. To mitigate this, senders could consider complimentary communication methods like MMS which allows you to provide more informative messages that include pictures, videos, and web links.

Final thoughts…

While some circumstances are clearly beyond a sender’s control, there are things you can do to give your messages the best chance of reaching your recipient. A general rule of thumb is to research SMS marketing rules and regulations as they apply in your state, interstate, and in the US and beyond. Once you’re aware of what is and isn’t allowed, you’ll have no problem running a successful SMS messaging campaign. 

A reputable business messaging provider will also have the local knowledge and expertise necessary to help you to navigate varying rules and regulations and will have best practice templates available so you can send with complete confidence that your messages will be received.