queued :

This means that the SMS you have sent has been queued internally for delivery.

sending : 

This means the SMS has been pushed by Exotel to the SMS Gateway and we're yet to receive the success/failed status.

sent :  

The SMS was successfully delivered to the recipient.

failed_dnd : 

The delivery of the SMS failed because the number belongs to the TRAI NCPR list. This is applicable only for promotional SMS.

failed :

The delivery of the SMS failed because of the following reasons.

  1. Telecom services not providing service for the particular number.
  2. End user has enabled message barring system.
  3. SMS got expired after multiple re-try.
  4. Failed to process the message at operator level.
  5. Handset doesn’t support for the incoming messages.
  6. Handset failed to get complete message.
  7. Problem with Handset.
  8. Subscriber is in busy condition.
  9. Failed to locate the number in HLR database. 
  10. Handset memory full.
  11. Mobile handset switched off.
  12. Subscriber’s operator not supported.
  13. Gateway mobile switching error.
  14. Given input was not recognized at subscriber’s operator level.
  15. Submission error or invalid input data.
  16. SMS is in retry state for the delivery. 
  17. SMS delivery failed since handset is not in good condition.