Pixel trackers are just small embedded images in the email that when they are fetched from a server, the server logs it. Pretty simple way to track whether or not someone has opened an email. It's my understanding that gmail however downloads all images and then serves them from Google servers to avoid this issue entirely.
Traditional email clients like Outlook/Thunderbird are susceptible to this kind of attack. That's why they often ask you before loading images.
Variants of "pixel trackers" still work fine on Gmail despite this. To this day a lot of marketing, recruiters and others are tracking when you open their message on Gmail.
No, disabling images breaks pixel tracking. One way to quickly sanity check a mail client's priorities is whether it gives you the option to disable images by default.
Some clients that don't allow you to disable by default: Polymail, Gmail on iOS, Inbox (Google) on IOS
Traditional email clients like Outlook/Thunderbird are susceptible to this kind of attack. That's why they often ask you before loading images.
https://smallbusiness.chron.com/set-email-tracking-pixel-493...