In HTML mails, the opening is measured using Tracking Pixels in images and links. Once the receivers email client loads an image or a link is clicked in the newsletter, the email campaign has officially started and activates the opening rate. Text-based email campaigns can only be counted if the recipient clicks on least on of the contained links.
The Opening Rate is listed in absolute numbers ("Numbers of Users") and percentages. Furthermore multiple openings are also being recorded statistically ("Total"). This number indicates that individual recipients opened the email campaign multiple times in their email client. By clicking on the openings per email address are itemized. The openings of the emails are shown in form of diagrams (at what date and time the emails were opened)