Why is my carrier blocking SMS messages from my long code number?

Long codes are regular 10-digit US and Canada phone numbers that can make and receive voice calls and send and receive SMS messages. Long codes are meant for person-to-person (P2P) communication. Long-codes are not appropriate for application-to-person (A2P) bulk messaging.

Carriers will block SMS messages:

  1. When more than 200 SMS messages are sent per day per long code number.
  2. When the ratio of incoming to outgoing SMS on a long code number is more than 1:3.
  3. For destinations other than US and Canada, when more than 1 SMS is sent every four seconds from a long code number.
  4. 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. 

Note: When sending SMS to US destination numbers, specify your US Plivo long code number in E.164 format. If you don't, you'll get the error message "This caller ID is not allowed for outbound message."

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