Viewing Details of Queued Notifications
Updated in 8.4
You can view the details of queued messages, both pending and failed, as follows:
From the Sidebar, navigate to Notifications > Notification Queue.
Double-click an e-mail message in the queue. The Email Message / Push Notification dialog box opens. In this dialog box you can view the details of the selected notification, including the error message if the message could not be sent out.