- When more than 200 SMS/day sent per Long Code Number.
- When the ratio of incoming to outgoing SMS on a Long 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.
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".