How Email Open Tracking Quietly Took Over the Web
Found on Wired on Monday, 11 December 2017
The tech is pretty simple. Tracking clients embed a line of code in the body of an email—usually in a 1x1 pixel image, so tiny it's invisible, but also in elements like hyperlinks and custom fonts. When a recipient opens the email, the tracking client recognizes that pixel has been downloaded, as well as where and on what device.
According to OMC's data, a full 19 percent of all “conversational” email is now tracked. That’s one in five of the emails you get from your friends. And you probably never noticed.
Every email client should block the loading of remote content by default; it has been abused by spammers for well over a decade now. Displaying email as plain text rather than ugly html also serves its purpose.