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SMS Message Filtering in the United States and Canada

This guide discusses filtering in the United States and Canada that can affect delivery of your Twilio Programmable Messaging SMS and MMS messages. In this guide, you will learn how and why messages are filtered, and options for improving your delivery rates.

Filtering occurs in order to enforce Twilio’s Messaging Policy or Acceptable Use Policy, and/or to comply with regulations and wireless carriers’ messaging policies. To learn more about how Twilio’s filtering system works as well as general information about filtering by wireless carriers, please see How Does Message Filtering Work?

For U.S. and Canada specific carrier filtering information, continue reading.

U.S. and Canada filtering overview

In the U.S. and Canada, application-to-person (A2P) type messaging was historically not allowed to be sent using local 10-digit long code phone numbers. Verizon Wireless began accepting A2P messaging via 10-digit numbers (A2P 10DLC) in January 2019. In 2021, Twilio and carriers (AT&T and T-Mobile, incl. Sprint) launched a registration-based A2P 10DLC solution, which permits A2P messaging via long code to United States recipients.

A2P traffic is how the industry refers to messages like automated alerts, notifications, one-time password (OTP) login codes, or any other kind of traffic originating from an application. For more information, please see What is P2P and A2P Messaging?

Filtering mechanisms

Filtering by wireless carriers

Wireless carriers in the U.S. and Canada apply message filtering for two reasons. First, carriers filter messages to protect mobile subscribers from spam and other forms of unwanted messaging. Secondly, some carriers apply filtering in order to detect and block A2P traffic that is being sent without A2P 10DLC registration.

Carriers in the U.S. and Canada use machine learning software systems to filter messages. These systems look at both message content and volume, and behave very much like email filtering systems. Messages receive a cumulative score based on factors including: how many messages have come from a phone number during a certain time period, how many similar messages have transited the carrier’s network, or do the message contents resemble known spam or unwanted messages.

In Twilio's experience, high opt-out rates and end user complaints also play a major role in carrier filtering. Because of this, the best thing to do to reduce the risk of filtering is to closely follow the rules in Twilio's Messaging Policy, in particular as they relate to user opt-in and opt-out.

Carriers in the U.S. and Canada usually report to Twilio when a message has been filtered. If you suddenly see that a large number of your messages are resulting in a status of Undelivered with a 30007 error, a filtering system has probably recently identified a pattern in your messages that triggered a block.

Filtering by Twilio

Twilio uses filtering to target message content or usage that is in violation of our Messaging Policy and Acceptable Use Policy (AUP). Twilio’s goal is to protect mobile users from fraud, spam, and other forms of unwanted messaging, as well as to comply with rules and regulations imposed by carriers and regulators.

Twilio's filtering systems are designed to allow A2P messaging, and filtering by Twilio is unlikely as long as your recipients have provided consent to receive your messages, and are not raising spam complaints or receiving a high amount of opt-out ("STOP") replies.

For more details on how filtering works, both by Twilio and by carriers, and how to avoid it, see How Does Message Filtering Work?

For tips and best practices for preventing filtering on your message traffic, see How do I prevent my Twilio messages from being filtered (blocked)?

Additional resources

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