What You Need to Know about SMS Deliverability
A common question that comes up when adding a new region or country to an SMS use case is “what percentage of the SMS messages that I send will be delivered successfully?” While this question is very reasonable, there are some nuances that need to be understood when formulating and interpreting the answer.
The ideal way to calculate this number would be to take the number of device confirmed SMS messages divided by the total number of SMS messages sent. The problem is that not all operators and routes support delivery receipts. A delivery receipt is a notification that the mobile device has received the SMS message. If a route doesn’t support delivery receipts but an operator it covers does, you may be able to find an alternative route that does support delivery reports for that operator. However, you’ll have to evaluate each route’s feature set and decide which ones (i.e. delivery receipts, character sets, message concatenation …) are the most important to you. Globally, this gets very challenging since the routes and operators frequently change and some operators falsely indicate delivery success.
If delivery receipts are not available, one alternative is to look at the acknowledgement of delivery to the route provider or mobile operator as the indicator of success. The problem with this strategy is that there are multiple reasons why an SMS message may fail as it travels between the mobile operator and the mobile user’s handset. Depending on your use case, this may be your only option. However, taking a step back and looking at your use case may reveal some better alternatives. If your use case is an interactive two-way SMS experience, then you can use the response SMS as an indicator that the previous SMS message was successfully delivered. Another alternative is to look at the business outcome. If your SMS message included a call-to-action such as going to a website and updating account information or making an online purchase, and that action was taken, then your SMS was successful.
Defining the Data Set
Another common issue with calculating SMS deliverability is the range of numbers to include. The most straightforward set of numbers to include would be all mobile phone numbers. However, some mobile phone numbers attempted may be misformatted, and some users have disabled SMS on their phone or are part of a a mobile virtual network operator (MVNO) (a special set of mobile operator) which may not support Short Code originated SMS. Other classes of numbers (such as landline numbers or VOIP numbers) have differing types of support for SMS. Google Voice numbers can receive Short Code SMS, while a Twilio number can’t receive Short Code SMS unless it is a Twilio Short Code. So, deciding exactly what question you are trying to answer is crucial for determining which set of numbers to include. Excluding MVNOs from your deliverability calculation doesn’t make sense if you are using Short Codes and want to reach all mobile phone users.
With all these complexities, an experienced and authentic SMS partner is a very valuable resource. They can evaluate your use case to identify the optimal mobile messaging strategy. They can also work with you to determine the right way to calculate your SMS deliverability success and explain the reasons for the variations you may see. You won’t be presented with a vague X% target with no explanation or an overly simplified explanation of one size fits all.