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How Does Carrier Filtering Work?

The networks in the US and Canada heavily filter traffic. This is an issue all gateways face.

How do carriers filter messages?

There is no standard way practice for carrier filtering and depends on each carrier. For some, filtering can range from a simple static list of prohibited terms to advanced machine learning systems that work in real time. Regardless of the system, carriers keep their filtering systems closely guarded secrets. In turn, ClickSend cannot say definitively how these systems work or why a particular message was filtered.

How do I know if my messages are being filtered?

ClickSend does not always know or predict when a message has been filtered by a carrier. Some carriers falsely report filtered messages as delivered to prevent spammers from reverse engineering filtering systems. In other cases, carriers will tell us that a particular message has been filtered. If we know that a message has been filtered, we will send this in the delivery report. 

How do I prevent my messages from being filtered

If you see an increase in carrier filtering you messages, these questions are a good guide for sending messages:

Is it a good user experience?

A confusing message to users might seem like someone they don’t know has their contact information. Suspicious users are more likely to report messages to their carrier, and when messages are reported to carriers it becomes very likely that future messages from that number or with similar content will be filtered. In some cases, the user may have forgotten that they requested the message. Also, how the message is formatted and written is important: overly long messages, overly capitalized messages, mysterious links, hyperbole, and using aggressive language can raise the level of suspicion users feel about a message.

Do users have clear opt out instructions?

If users do not understand how to opt out, they may feel they have no choice but to contact their carrier to request that messages are blocked.

Can traffic be sent via a shortcode?

If you are sending large numbers of identical messages, the carriers in the country you are sending to may require that this traffic be sent from a shortcode.

Is a single number being overworked?

In countries where rate based filtering takes place, sending too many messages from a single phone number or alpha sender ID during a time period could cause that phone number or sender ID to be blacklisted. See the country specific pages to see more specific information about our experience with filtering in a country.

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