The statuses below are exclusively for Chargebee SMTP users and signify whether the email has been delivered to the customer.

Delivered: The email has been successfully delivered to the customer.

Opened: The delivered email has been opened by the customer. For this to work, you need to enable the Show email opens option under Settings > Configure Chargebee > Email notifications > Change SMTP settings.

Dropped: The email has not been delivered to the customer. Possible reasons might be the user unsubscribing from your emails or the email being flagged as spam by a third-party spam application.

Bounced: The email has not been delivered due to server denial. A possible reason might be the incorrect "Send to" address.

Note: 
For Dropped and Bounced emails you can find the exact reason for non-delivery by hovering over the exclamation icon.