This story explains how to tell which emails are tracking users. The senders of these emails want to know whether the information sent to the user has been opened. Usually, a tracking pixel embedded in the email is how most people monitor whether the email is open. Once the user loads the hidden tiny single-pixel image, it returns to the base. The easiest way to stop tracking emails is to cancel `Load remote content in emails. If users want further control, they can use extensions in some browsers. – Yansong Wang
A tracking pixel, embedded somewhere in the email, is used to monitor whether and when the receiver opens up the email. Users can disable "Automatically load remote content in messages" in the general email account settings to prevent being tracked. Also, users can use extensions like "Ugly Email" and "Trocker" of chrome to spot tracking emails. -Zheyu Ren