1. Access your reports. Begin by selecting your event. Hover over Reporting and, under Reports, click Standard Reports. Click Email Rates by Email. It may take a few minutes for your report to process.
2. See how many were delivered and opened. The Totals section summarizes the following for every email sent from this event:

• Sent shows you how many successfully arrived in an inbox.
• Undeliverable tells you how many bounced back.
• Undeliverable Rate divides the number you sent by those that bounced. You want this number to be low, around 10%.
• Opened shows you how many recipients actually opened your email (and presumably read it).
• Open Rate divides the number you sent by those that were opened. The higher the better. The average open rate for Cvent emails is 28%.

For full details and other related topics, checkout the complete tutorial from Cvent.