Delivery of a message depends on the filtering system carriers use. When subscribers receive messages they find objectionable, they may file complaints or report the carrier to governing bodies, seek damages, or simply stop being a customer. All of these things reduce the revenue of or increase costs for carriers. Thus, it is in the best interest of carriers to protect their subscribers from what they consider to be objectionable content.
How do carriers filter messages?
There is no standard practice for carrier filtering across all carriers. 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, we cannot say definitively how these systems work or why a particular message was filtered.
How do I prevent my messages from being filtered?
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.
Carriers in the U.S. and Canada appear to be using adaptive (machine learning) software systems to protect their users. These systems factor in both the rate of send, as well as the content of the messages and behave very much like email filtering systems. Messages receive a cumulative score based on how many messages have come from a phone number during a time period, how many similar messages have transited the carrier’s network, or if the message contains content that makes it a high match for spam. Time periods are measured by the second, minute, hour and day.
I think my number has been blacklisted by a carrier. Can I get it removed?
No. However most blacklists in the US and Canada use a “cooling off” period, which means that most numbers will automatically be removed from the blacklist after a period of time. This period of time varies based on how many messages were blocked by the carrier from this number, and carriers do not share this time period with us.
Can I get my messages whitelisted by the carriers?
US Carriers do not whitelist messages from long code numbers. If you are sending many messages with identical content to a large number of users, you are at high risk of having your messages filtered by carriers.