How to view a report of the Emails Sent?

For email(s) you just sent:

As soon as you click on send, a confirmation box will appear with the text Success message. On the confirmation box, you will see a button which says View Report. Click on it and the report will be downloaded to your local machine in Excel (.XLS) format.

For already sent email(s):
Please select the person to whom you sent the email and scroll down to the section called 'Participant administrator Emails' 

or 
From the left side menu go to Reports open  Web Reports in the sub-menu and now on the dropdown select  - 6.51 Participant Emails Report.