“I JUST CAME across this email,” began the message, a lengthy overdue reply. However I knew the sender was lying. He’d opened my email nearly six months ago. On a Mac. In Palo Alto. At night.

I knew this because I used to be running the e-mail tracking service Streak, which notified me once my message have been opened. It informed me where, when, and on what sort of device it absolutely was read. With Streak enabled, I felt as an inside trader whenever I glanced at my inbox, privy to details that provided me with maybe a tad too much information. And That I certainly wasn’t alone.

There are several 269 billion emails sent and received daily. That’s roughly 35 emails for everyone on the planet, every day. Over 40 % of those emails are tracked, based on research published last June by OMC, an “email intelligence” company which builds anti-tracking tools.

The tech is pretty simple. Tracking clients embed a line of code in your body of an email-usually in a 1×1 pixel image, so tiny it’s invisible, but in addition in elements like hyperlinks and custom fonts. When a recipient opens the email, the tracking client recognizes that pixel has become downloaded, in addition to where and on what device. Newsletter services, marketers, and advertisers have tried the procedure for a long time, to accumulate data regarding their open rates; major tech businesses like Twitter and facebook followed suit inside their ongoing mission to profile and predict our behavior online.

But lately, a surprising-and growing-variety of tracked emails are being sent not from corporations, but acquaintances. “We have already been in touch with users which were tracked by their spouses, 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 from the emails you obtain from the friends. And you probably never noticed.

“Surprisingly, while there is a vast literature on web tracking, email tracking for gmail has seen little research,” noted an October 2017 paper authored by three Princeton computer scientists. All this signifies that billions of emails are sent every single day to huge numbers of people that have never consented by any means to be tracked, but they are being tracked nonetheless. And Seroussi believes that some, at the very least, will be in serious danger as a result.

As recently as the mid-2000s, email tracking was almost entirely unknown to the mainstream public. Then in 2006, a young tracking service called ReadNotify made waves whenever a lawsuit stated that HP had used the product to trace the origins of the scandalous email who had leaked towards the press. The intrusiveness (and simplicity) in the tactic came as something of any shock, although newsletter services, salespeople, and marketers had long used email tracking to collect data.

Seroussi states that Gmail was the ice breaker here-he points back to the times when sponsored links first started showing up within our inboxes, based on tracked data. During the time it seemed invasive, even unsettling. “Now,” he says, “it’s common knowledge and everyone’s fine with it.” Gmail’s foray was the signal flare; when advertisers and salespeople realized they too could send targeted ads according to tracked data, with little lasting pushback, the practice grew more pervasive.

“I have no idea of any single established sales team in [the online sales industry] that fails to use some form of email open tracking,” says John-Henry Scherck, a content marketing pro and also the principal consultant at Growth Plays. “I think it will likely be a point of time before either everyone uses them,” Scherck says, “or major email providers block them entirely.”

That’s partly concerning spam. “Competent spammers will track any activity on your own email because they often buy entire lists of addresses and will actively try to rule out spam traps or unused emails,” says Andrei Afloarei, a pnifcc researcher with Bitdefender. “If you click on any link in just one with their messages they will likely know your address will be used and may actually cause them to send more spam the right path.”

But marketing and internet based sales-even spammers-are will no longer in charge of the bulk of the tracking. “Now, it’s the major tech companies,” Seroussi says. “Amazon continues to be utilizing them a great deal, Facebook has become using them. Facebook is the number one tracker besides MailChimp.” When Facebook sends an email notifying you about new activity on your account, “it opens an app in background, and today Facebook knows where you stand, the unit you’re using, the very last picture you’ve taken-they get everything.”