nexmo sms deliverability guide

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Nexmo SMS Deliverability Guide


SMS has a mission-critical role in modern business many high-priority applications, alerts, and content depend heavily on an SMS being delivered in a timely manner. But what if your server goes down and your monitoring system fails to alert you? Or what if your credit card is stolen or someone hacks into your email account you want to know the second it happens, right? SMS is considered to be one of the safest channels for the transmission of critical information to a phone. It works on any handset, in any country, and it is opened more often by recipients than other channels. But its deliverability is not flawless. The telecom industry is not fully inter-operable and the optimal path for delivery is not always the one you are using. Luckily, there are proven techniques to improve your delivery ratios. As a cloudbased API that lets developers and enterprises send and receive high volumes of SMS at wholesale rates, we at Nexmo are uniquely positioned to understand these techniques. As such, weve put together this guide an overview of the main issues and how to address them when designing your application. Lets get started.


Here are the most frequent issues preventing an SMS from getting delivered: Carriers Spam Filters: Simply put, carriers got fed up with the spam their subscribers were getting. Most carriers in developed markets prefer to use regulations to control the flow of spam. In developing markets, however, technology is used to filter out unwanted texts. These filters, however, areWhich carriers filter and how? Get the full list of carriers that filter by visiting Find tips on how each filter works and which criteria are being used to block messages.

Nexmo SMS Deliverability Guide

not perfect and can lead to filtering legitimate SMS traffic, as well. Some filters even send back a fake handset delivery confirmation. You think your message is delivered, but it is not. Furthermore, filter technology is in constant evolution, and associated algorithms change constantly. Keeping track of which carriers filter and how is a complex task.

More Hops Mean More Points of Failure: With each additional hop to reach the final subscriber, the probability of failure increases. It is common that your SMS crossed 5 or 6 gateways before reaching its final destination. Old telecom protocols that connect these gateways do not always work well and sometimes create congestion, leading to increased latency and, ultimately, loss of messages.

Sending The Wrong Content: Not all phones support all languages. For instance, sending a Chinese message to a French phone will get to the handset but will not display to the user. Sending binary messages to an iPhone wont work, either. Certain carriers also filter some keywords (such as the carriers own name) to prevent brand theft and scams.

Did you know? iPhones dont display WAP Push messages.

Nexmo SMS Deliverability Guide

Phone Cant Receive SMS: There are manyWhich markets let me set the sender? Learn about carrier-specific restrictions on sender IDs and more on

number of reasons that can prevent a phone from receiving an SMS that it would be able to receive under normal conditions, including the phone being out of reach, a full memory, roaming, temporary disconnection, the number not existing anymore, and so on.

Portability Failure: A lot of phones get ported everyday from one network to another. The number will still look like the original network but the real network has changed. To address this, carriers have introduced network look-ups that provide them with the real network before sending the message. This guarantees that the SMS is routed correctly. The process, however, is not perfect. Network look-ups are expensive, and many providers dont do them everywhere. Some carriers, in fact, still dont even support these looks-ups at all. Additionally, some portability databases only get updated every 24 hours.

Now that we understand why some messages dont get delivered, lets take a look at some proven techniques to improve success ratio. To start, well look at a variable that can greatly influence delivery setting the correct sender ID.

Nexmo SMS Deliverability Guide


But, What Is A Sender ID? When someone texts you, the sender ID is set to that persons phone number. But this alphanumeric variable can be set in any 15 digits or 11 characters with no space. Brands love this because it enables them to set their brand name as the sender ID. In some markets, such as North America or Brazil, the sender ID cant be changed, but in most markets it can be modified.

Use Numeric Sender IDs: Avoid using alphanumeric sender IDs; most carriers spam filter alphanumeric senders. Instead, use numeric senders in international format (e.g. 397525856425).

Did you know? You can acquire low-cost, valid virtual phone numbers from Nexmo that be set as your numeric sender IDs.

Randomize Sender ID: Some carriers will block repeated messages from the same sender, be they numeric or alphanumeric. To achieve optimal performance, get enough numeric senders in international format and then rotate them randomly for each message you send.

Avoid Using UK, Swedish, or Local Senders: Carriers are used to receiving a lot of spam messages from the UK and Sweden, so they block a lot of them. They also block local senders to avoid the spoofing of identities or to force their local personto-person traffic not to take certain routes.

Nexmo SMS Deliverability Guide


Lets talk now about the body of the message itself. There are a few tactics that you can use that will help you get your message across.

Dont Spam: Not only is it illegal, more often than not, it doesnt work. Most likely the message will not arrive at the handset and you will still be stuck paying for it. Spam filters have become very good at detecting spam attacks.

Use the Right Encoding: When sending in languages such as Chinese or Arabic, make sure that you format your message correctly and set the content type to Unicode. Try to adapt the language to the market, i.e. dont send Arabic to a Brazilian phone number. The handset probably wont be able to read it.

Randomize the Body of the Message: As weve seen with sender IDs, it is better to randomize the body of the message, if you can. If you are sending a campaign or password code, come up with more than one version of the content and change it randomly. For example: Message 1: Your Pin Code is 2234 Message 2: Please enter 6765 into your application to verify your accountTOOLS TO MEASURE SMS DELIVERABILITY

Now that we have a better understanding of how to boost success ratio, its time to learn how we can actually measure it. At Nexmo, we use a few trends to track Quality of Delivery (QoD) performance: Success Ratio: This is the number of messages sent / received. Any serious SMS API should provide a handset delivery confirmation where supported. The ratio itself is important, but what are more meaningful are its variations. Some carriers dont provide delivery confirmation, or provide them sporadically. Therefore, it is moreNexmo SMS Deliverability Guide

important to track variations for a given network rather than an absolute figure. Another ratio DLR ratio that could be viewed as meaningful is the number of messages sent that receive a status (be it delivered or failed). This ratio measures how well the route is performing. A healthy route provides statuses for over 97% of messages.

Delivery Latency: With handset delivery confirmation comes delivery latency! Again, the important thing to measure here is the variation in latency, rather than the absolute figure. The reality is that not all carriers have the same quality of infrastructure, and some prioritize outbound traffic on a delivery confirmation path. Plus, some handsets take more time to acknowledge the reception of the message than others. And finally, if a phone is out of reach, then the latency figure will be statistically biased because the message will be delivered only when the phone has reconnected to the network. Track changes, not absolutes! Application Specific KPIs: The ultimate measure of performance is your application specific KPIs. For instance, if you are sending passwords to verify phone numbers, you should track the ratio of conversion between SMS sent and users registered. For marketing campaigns, you could measure returns. If your application is two-way, then track replies, etc.

Did you know? With Nexmo, there is no need to build your own Quality of Delivery KPIs we do that for you. Get connected to your account and track KPIs in real time!

Nexmo SMS Deliverability Guide


Scale with REST rather than SMPP: There is a myth in the wholesale SMS industry that you can only achieve scale with SMPP. It is possible to build a REST integration that rivals a well put together SMPP integration, and it will blow a badly built SMPP integration out of the water.

Use one hop provider: At high volumes, performance (measured by delivery ratio and latency) degrades exponentially with each additional hop. Get closer to the source and ask your provider about their sourcing strategy.


Format the destination address: Make sure to format the to field in international format. Refer to the ITUs International Numbering Resources.1 Dont trust the user to insert the right forma