Message Read Confirmation is a premium feature that shows you when an email you sent has been read. You must have an upgraded account to add premium features.
Want to see if your message has been read?
From the left menu, under Inbox, click Sent to view your sent messages. If your message has been read, the envelope icon next to the message will have a green checkmark. If you don't see the checkmark, the message hasn't been read yet.