Chrome extension warns you when an email you receive in your Gmail inbox have the ability to track you, and it even works before opening the email. Ugly Email works only on Google’s Chrome browser, so you need to make sure that you’re using Google Chrome as your web browser while using the service. It doesn’t store, save, or transmit any data from your Gmail account or computer; everything takes place on the user’s end. It is currently effective against only three companies — Yesware, Bananatag, and Streak — but will continue to add more tracking services to its list.
Source: https://thehackernews.com/2015/03/email-tracking-software.html