How are open percentage rates calculated?

Opens are tracked by transparent pixel included in the HTML version of your email campaign. When the email is opened, the pixel loads as well, and lets our server know who loaded it. This type of tracking is not available for the text version.; opens can only be tracked for recipients who view the HTML version of your email. Generally, Text only recipients make up a very small portion (on the whole, less than 3%) of your entire list.

The open rate is determined by the number of opens divided by the number of HTML/Text emails sent.