Actually no it's not, most read-trackers use invisible images in the email body. When you open the email the images all load from their remote server, and thus they know you opened the email, and when.
You can work against this by disabling images, or you can add a tracker list I made to your adblocker!
You can work against this by disabling images, or you can add a tracker list I made to your adblocker!
https://github.com/leavemealone-app/email-trackers