See how many people viewed your email with the email campaigns report
After sending out an email to your attendees you can check to see how many people have opened the email, who opened it and when. Start by going to Charts & Reports > Email Campaigns.
Your most recent email campaigns are shown here along with an overview of each email, including the number of opens, opt-outs  and click-throughs . To view details click on the hyperlinked number under Opened .
Here you'll find a list of email recipients along with their email address , when they last opened the email , and how many times they viewed it .
The recipient's name won't appear on the Open Rate report if the email wasn't opened.