In just one click you will see when the email sent from the application was opened and clicked by the recipient. Morever, you can track if your attachments (i.e. offers) were opened.
You can see opens by clicking on the green eye in your sent message.
You can see clicks or downloads by clicking on the green dot next to each link or attachment in your message. Example:
GDPR requires that recipients have opted in to the collection of tracking data