Good article on the history and practice of e-mail tracking:
The tech is pretty simple. Tracking clients embed a line of code in the body of an email — usually in a 1×1 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. Newsletter services, marketers, and advertisers have used the technique for years, to collect data about their open rates; major tech companies like Facebook and Twitter followed suit in their ongoing quest to profile and predict our behavior online.
But lately, a surprising — and growing — number of tracked emails are being sent not from corporations, but acquaintances. “We have been in touch with users that were tracked by their spouses, business partners, competitors,” says Florian Seroussi, the founder of OMC. “It’s the wild, wild west out there.”
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.
I admit it’s enticing. I would very much like the statistics that adding trackers to Crypto-Gram would give me. But I still don’t do it.