SMS Delivery: 7 Factors that Affect Deliverability via Searchbug

SMS Delivery: 7 Factors that Affect Deliverability

Short message service, or SMS, is very similar to a text message. SMS only has the ability to send text, however, not images or videos. And SMS messages are usually limited to 70 characters. You send text messages successfully all of the time. So why should you worry about SMS delivery?

SMS delivery refers to the rate messages get delivered versus bouncing. If you have a high delivery rate, you are very good at getting messages to their destinations. A high delivery rate establishes you as a trusted sender and increases your chances of continuing to successfully send messages.

A low SMS delivery rate, as you can imagine, means a large portion of the messages you send do not make it to their destinations. They bounce and are categorized as undelivered. This hurts your sending reputation and could raise a red flag with spam filters making it more difficult for you to improve deliverability.

In this article, we cover 7 factors that could cause your messages to be undelivered. Then, we’ll tell you how you can prevent bounces and improve deliverability. You have to remember that sending mass marketing SMS messages is quite different from the everyday text messages you send to your friends.  

7 Factors that Affect Your SMS Delivery Rate

1. Invalid Numbers

Your SMS delivery will suffer if you send messages to numbers that are invalid. It seems pretty obvious, but how many invalid numbers do you have in your database that you aren’t aware of?

An invalid phone number is one that cannot be reached either because it is formatted incorrectly, doesn’t exist, or is disconnected. There are a number of ways invalid phone numbers can enter your database.

First, invalid phone numbers could be the result of data entry errors. Either you, your team, or your customer mistypes the number into the database or web form and no one is the wiser. 

Second, customers can knowingly provide disconnected or fake phone numbers instead of their real numbers in order to avoid receiving marketing calls, protect their privacy, and/or ease their fears of potential scams. 

Last, phone numbers that were once active and legitimate at the time of entry can become abandoned or disconnected. For example, when someone switches phone carriers, his or her original phone number might become recycled for someone else to use if it cannot be ported to the new carrier.

Unless you regularly check your list of customer phone numbers, you could be wasting time and money sending SMS campaigns to numbers that will never receive them.

2. Spam Filters

Some cell phone carriers have spam filters (or carrier filters) that block messages that seem sketchy. This protects their customers from receiving unwanted messages and smishing campaigns. 

Smishing is when a fraudster sends a text message disguised to be legitimate in an attempt to gather sensitive, personal information from the recipient. Phishing is a harmful email campaign while smishing is a harmful SMS campaign.

These filters look for opt-out instructions (more on this later) and the number of messages sent compared to the amount of time between messages. For example, if you send too many messages too fast, it could raise a red flag with spam filters.

Person to person (P2P) and application to person (A2P) messages are filtered differently. Cell phone carriers can identify whether a message is sent from a personal number or from a mass text messaging application. A2P messages are more likely to be filtered than P2P messages due to the volume of messages sent. Filtering is done to prevent spam.

3. Receiving Device Issue

If you are sending messages to landline or VoIP numbers, your SMS delivery will fail because these line types do not support SMS. 

Additionally, if a mobile device is roaming, or connecting to a network outside its own, you might not receive a delivered report.

Finally, you might experience a “soft bounce” when a message temporarily cannot be delivered. If a number is out of range of service or is turned off, the message might not be delivered when you send it but will eventually be delivered once the device is back in range of service and/or turned on.

4. Routing Factors

Cell phone numbers are owned by carriers, not by the owner of the cell phone. So if you can identify the carrier of each of the numbers in your database, your messages will be delivered more efficiently and effectively.

The software you use to send your SMS messages will need to know the carriers of the cell phone numbers you send to in order to properly route the messages. It’s like a fork in the road: when an application sends messages, it has to be able to identify the proper route to get each message to its destination.

Most text messaging software needs to know the current cell phone carrier for each cell phone number and won’t have its own carrier lookup abilities. Since phone numbers can be ported, meaning the number owned by one carrier can be transferred to another carrier without changing the number, using the original carrier for all numbers can cause messages to be undelivered.

The final issue with routing is if a certain network doesn’t allow the delivery of a message. Some network providers offer services that reroute messages, but without it the message remains undelivered.

5. Incorrect Encoding

Like we mentioned before, there is a certain number of characters that is supported by SMS. However, there are two options here. Encoding determines the number of characters that an SMS message can support. Unicode supports 70 characters while GSM supports 160 characters.

So if your message is sent using Unicode and you exceed the number of allowable characters, your message probably won’t get delivered. The same goes for GSM, only you have a larger limit and a smaller chance of exceeding it.

If you are sending messages in the U.S., Unicode is standard. GSM messages could become jumbled and unreadable which would be bad for your campaign. Plus, some carriers might refuse to deliver GSM messages altogether either because of that possibility or because they aren’t easily supported.

6. Number Type

There are four different number types that can be used to send SMS messages: short code, toll-free long code, local long code, and 10-digit long code (10DLC). Each has its own advantages and limitations (find out more here). 

If you use a free online SMS messaging application, there’s a good chance your messages are being sent using email which is a form of long code messaging. Long code messaging is what you use to send a message from your personal number to your friends, family, colleagues, etc. It’s intended for private use between individuals.

So if you’re sending messages in bulk from what’s identified as a long code number, you’re going to run into some obstacles. First, you can only send 1 message per second. Second, you can only send 500 messages a day. Third, if you err and exceed this, your number could be blocked. And finally, to even attempt to send a message this way, you need an approved virtual number.

Sending from a long code number limits the number and speed of messages you send and could result in your number becoming blocked. This will take time to fix and could interfere with future campaigns.

7. Gray Routes

A gray route is a workaround to avoid paying third party network operators to send messages. Instead, gray routes use unauthorized networks to deliver messages.

Legitimate carriers won’t do this. But network operators that are contracted by carriers might use gray routes to avoid certain costs. So SMS providers that contract out aspects of their network infrastructure could unknowingly be sending messages over gray routes.

If you’re thinking this should be a spam filter red flag you’d be correct. This is why messages sent over gray routes have a high chance of being undelivered.

How to Prevent Errors and Improve SMS Delivery

1. Validate Phone Lists

To catch and remove those invalid phone numbers that make their way into your database, you need to validate your phone lists. There are two tools you can use: phone validation API and batch phone verification tool.

A phone validation API verifies phone numbers at the point of entry. If a phone number is invalid, the API will know and won’t allow it to enter into your database. 

Batch phone verification allows you to check numbers currently in your database. Either you haven’t ever validated your list before or you want to conduct regular list cleaning. 

List cleaning is very important because phone data changes over time. Numbers that were once valid when entered could eventually become disconnected or reassigned. So you want to verify your existing list at least a couple of times a year.

By validating your phone list, you ensure that you only spend resources sending SMS messages to valid, active numbers. These tools can also identify line type and carrier so you can organize your data. Avoid wasting time and money sending messages to landlines and ensure accurate delivery to cell phones by properly routing your messages.

2. Validation Error Messages

Rather than losing customers and leads to typos, you can use validation error messages to help get valid phone numbers added to your list. For example, if a user enters his or her phone number but accidentally leaves out a digit, the phone validation API will discard it and you lose out on that user’s business.

However, if the webform presents an error message before the user submits the incorrect information, he or she has an opportunity to fix it before submitting. This way you have a better chance of retaining that data.

3. Provide Opt-Out Instructions

To help prevent your messages from being caught by spam filters, you need to provide opt-out instructions in your messages. Consumers must consent to receiving SMS marketing messages, so providing opt-out instructions is a common SMS regulation requirement. 

You also don’t want to face TCPA fines by messaging numbers that have not opted in. This is another reason why it’s important to regularly verify numbers in your list. One user might opt in to receiving SMS messages from you to his or her number, but if that number gets reassigned to a user who hasn’t opted in, you could face serious consequences.

So make sure the recipients of your messages know how to end them if they choose to.

4. Collect Phone Numbers Using a Keyword

One effective way of ensuring you have both customer consent and an active number is to have users respond to your message by texting a keyword back to you. You also know, then, that the number is tied to an SMS capable device.

For example, your message could read: Type CONTINUE to receive updates from us. Until a user responds to the message with the word “continue,” no more messages should be sent to that number.

5. Avoid Certain Keywords

Spam filters look for certain keywords to help protect users. Terms like “free,” “guarantee,” or “limited time” can be considered too salesy or sleazy and indicate potential spam.

Keep your messages personal and friendly instead to connect with your users, encourage continued subscription to SMS receipt, and improve your SMS delivery rate.

6. Use Short Code Messaging

We talked about the disadvantages of using long code messaging. One alternative, then, is short code messaging. Short code was designed specifically for mass messaging. 

Short code allows you to send millions rather than hundreds of messages a day and 500 messages a second as opposed to one per second. And since marketing is the intended purpose of short codes, they are pre-approved for you and therefore not subject to spam filtering.

So with a short code SMS service, you can send more messages quicker and ensure delivery to SMS enabled devices and active numbers. 

7. Switch to a Better Carrier

Plain and simple, you want to work with a carrier that can support your SMS messaging needs. Avoid partnering with carriers that use gray routes or contract out to companies that do. Use A2P messaging, try to get assigned a short code, and make sure your messages are sent via Unicode.

The Importance of SMS Delivery

Unless you cover all of your bases, you risk sending messages that have a low chance of getting delivered. The lower your SMS delivery rate, the less and less messages you will successfully get to the recipients. It is an endless cycle. Your SMS delivery rate, therefore, improves as the number of successful messages you send increases.

This is good news for your future campaigns. An SMS marketing strategy is a money-maker, but you also save time and money by avoiding errors. Furthermore, you ensure TCPA compliance by following all of the guidelines set forth by the FTC regarding SMS marketing. 

So it’s more than worth it to know your data inside and out. Searchbug can help. Try our phone validation API and batch phone verification tool today!



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