At around 08:45 am MDT we deployed a change to further our support of 10DLC. Shortly after the deploy we stopped getting "Message Delivery Receipts" from our SMS providers. We rolled back our changes at around 12:30pm MDT and are investigating the cause. You may see messages that you sent within this time frame have their delivery status update to "Unknown". The messages were all successfully sent, there is no need to attempt to retry sending.