Long codes are regular 10-digit US/Canada phone numbers that can make/receive Voice calls as well as SMS messages. Long codes are meant for Person-to-Person (conversational) communication. Long-codes are not recommended for one direction bulk messaging use cases.

The following are the usual characteristics of Application-To-Person SMS messages, which when present will be blocked by carriers:

  1. When more than 200 SMS/day sent per Long Code Number.
  2. When the ratio of incoming to outgoing SMS on a Long Number is more than 1:3.
  3. For destinations other than US/ Canada: Messages will be queued if sent more than 1 SMS/4-second/Long Code Number.

        4. When the same message sent to the same user within 5-10 seconds of the first message.

Other factors that can result in SMS blocking: 

  • When using repetitive URL's and keywords, shortened links(such as bit.ly) in the SMS content.
  • Multi unit messages. 

Note: When sending SMS to US destination numbers please use your US long-code number(from Plivo account) in international format. If not, you will get this error: "this caller id is not allowed for outbound message".