Long codes are regular 10-digit US and Canada phone numbers that can make and receive voice calls and send and receive SMS messages. A2P SMS is text messaging between an application and an individual. It typically involves automated content sent by an organization or business to a subscriber. A2P is commonly used for confirmations, alerts, marketing campaigns, and two-factor authentication (2FA).
Carriers will block SMS messages:
- When more than 200 SMS messages are sent per day per long code number.
- When the ratio of incoming to outgoing SMS on a long code number is more than 1:3.
- For destinations other than US and Canada, when more than 1 SMS is sent every four seconds from a long code number.
- When the same message is sent to the same user within 5 to 10 seconds of the first message.
Other factors that can result in SMS blocking:
- The use of repetitive URLs and keywords or link shortener URLs in the SMS content.
- Multiunit messages.