There are several stages a SMS message goes through before it is delivered to the customer. You can find the current status of a SMS message by going to Admin icon () > Channels > Text > History. This article goes through each status and what they mean.
accepted - When a request is first sent to Twilio through an API request to create a new text message, this is the first response received by the client. Twilio will now try to associate the correct ‘From’ phone number for the message.
queued - Once Twilio finds the correct ‘From’ phone number, the message is now queued to be sent out.
sending - Twilio will now start the process of sending out your message to the nearest upstream carrier in the SMS network.
sent - The message was successfully sent to the nearest upstream carrier and has been accepted for delivery.
delivered - Twilio has received confirmation from the upstream carrier that the message was delivered to the recipient.
failed - The upstream carrier did not accept the message from Twilio.
received - Each incoming message to your Zendesk Text number will have a received status associated with it.
undelivered - The message was not delivered and can be caused by a variety of reasons listed here.