If a Message has a Delay, it will first be sent to Scheduled. (If there is no Delay, when a message is triggered it will be sent directly, and show up in the Sent list.)
Scheduled Emails gives you a list of what’s queued to be sent.
Once sent the message will show in Sent.
You can search by various fields, and also click to get more info on the message.
You can delete messages from the queue if desired. If you want to delete in bulk, you can search for a particular criteria and then use the Delete Selected Results button to remove all messages meeting that criteria from the queue.