In some cases, message filtering can affect delivery of your Twilio SMS messages. This is done to enforce Twilio’s Messaging Policy and Acceptable Use Policy, which are designed to prohibit spam and other forms of abuse, and to comply with regulations and wireless carriers’ messaging policies.

Filtering of your outgoing Twilio Programmable SMS messages can vary somewhat between carriers and countries. We have compiled a lot of helpful information in How Does Message Filtering Work? to help you understand why a message might have been filtered. In addition, we have summarized some important rules and guidelines for avoiding filtering in the article How do I prevent my Twilio messages from being filtered (blocked)?