The industry of email tracking services (including Mailtrack) use images as a tracking system. The most effective way to avoid being tracked is not allowing images to be displayed in the emails you receive. In order to do so, please, check the settings of your email service and turn off the option to display images. See here instructions to turn off images for Gmail.
Please, be aware that even if you receive emails with the Mailtrack signature ("Sender notified by Mailtrack") you will not be tracked.