Wireless carriers in the U.S. and Canada filter messages for two main reasons. First, they want to protect mobile subscribers from spam and unwanted messages. Second, some carriers use filtering to detect and block A2P (Application-to-Person) traffic that hasn’t been properly registered with A2P 10DLC.
Carriers use machine learning systems to filter messages based on factors like content, volume, and sender behavior—similar to how email filters work. These systems assign a cumulative score to messages, considering factors such as the frequency of messages from a number over a specific period, the volume of similar messages on the network, and whether the message content looks like spam.
In our experience at Heymarket, high opt-out rates and user complaints are also significant factors in filtering. To minimize the risk of filtering, it's crucial to follow Messaging Best Practices especially around opt-in and opt-out practices.
If you notice a sudden increase in messages showing as Undelivered with "filtered" in the error, it likely means a filtering system has flagged a pattern in your messages and applied a block. Carriers typically report this to Heymarket, so it's essential to monitor and adjust your messaging practices to stay compliant.