To know if a message has been delivered follow these steps:
1) Select a conversation from the Conversation List
2) A green check will appear next to a message that has been successfully delivered.
3) The same area next to an outgoing message will also display status messages such as whether a customer is pending an opt-in, or if the message is scheduled for delivery at a later date.
4) Message delivery may appear as "Failed" in the event a message could not be delivered to the recipient. In most cases, this is due to the recipient's phone number not accepting text messages (e.g. old landline numbers), or an incorrect/non-existent phone number.