Long codes are regular 10-digit US/Canada phone numbers that can make and receive voice calls as well as SMS messages. Long codes are meant for person-to-person communication. Long-codes are not recommended for bulk messaging.
The following characteristics of application-to-person SMS messages will cause your message to be blocked by carriers.
- When more than 200 SMS 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/ Canada: messages will be queued if sent more than 1 SMS/4-second/long code number
- When the same message is sent to the same user within 5-10 seconds of the first message.
Other factors that can result in SMS blocking:
- The use of repetitive URL's and keywords or 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 message: "This caller id is not allowed for outbound message"