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Quiubas SMS Deliverability Guide

Have you ever wondered why an SMS fails to deliver? This is a quick guide to understand how SMS networks operate and how to improve SMS delivery ratio; itncludes key tips on building reliable SMS applications.

Connection Quality

Most aggregators or SMS gateways relay on gray routes to deliver SMS; this is most common when sending SMS to Latin American countries, Mexico, Colombia, Chile and Brazil are big targets of gray routing SMS deliveries.

Basically, a gray route is an SMS route that manages to offer an extremely cheap pricing by making arrangements outside of the licensed international telecoms companies. This is mostly accomplished by the use of SIM farms or SIM servers.

When you buy a cheap route, you realise that your traffic is delivered through countries like India, Russia or the Far East; these types of routes use several hops to reach the final recipient, SMS get clogged up on an overloaded connection, as most likely more than 2 companies are involved in the process.

SIM farms and gray routes may be cheap but they frequently just disappear without notice and blocking the route, then your SMS messages stop been delivered until your provider finds a new route.

Quiubas has the only direct SMS connection to carriers in Mexico, this means we can guarantee your traffic delivery.

Before choosing an SMS provider, we advise you to ask him what type of routes they use.

Spam Filters

To fight the large number of unsolicited text messages, carriers opt to filter out sms messages they consider spam. Filtering out messages, can cause real messages to be undelivered, even more, generating a valid delivery report.

Content Type

Not all phones support all languages. An example would be a message sent in Arabic to a French phone will most likely not be displayed correctly on the phone. Depending on the carrier, some keywords are used for filtering, such as the carrier’s name, to avoid scams and brand identity theft.

Phone cannot receive sms messages

SMS is perhaps the most reliable way to send text messages. However, there are times when the message does not reach the recipient’s device, even after succesfuly submitted to the carrier. Some of the reasons that can cause a message not to be delivered are:

  • Phone is switched off or out of reach
  • Memory is full
  • Roaming
  • Disconnected phone
  • Number no longer exists


As it has become very common to have mobile services to be ported from one network to another and numbers not changing, the phone number can still carry the original network codes. Carriers have introduced network look-ups – HLR – that provide them with the real network for a number before sending a message, so that they can identify the right route for sending it. The down side is that network look-ups are expensive, they are not updated on a regular basis and some carriers don’t support them.