While the tech companies harvest our data to sell ads, in recent years email services have been off limits. That limit has just been crossed with the disclosure that Verizon is now promoting a new service to advertisers where they continually scan the 200 million inboxes of Yahoo Mail users. Yahoo Mail is a part of Yahoo that Verizon recently acquired under their Oath brand. Oath/Verizon told advertisers that they search the mail for clues about what people might buy or be interested in buying. They are doing the same with AOL Mail, which Verizon also owns.

Among all of the U.S. email providers, these are the only mail services being exposed to this intrusion. In the past, Gmail also scanned users’ emails but the company terminated that practice last year. Of course, Google has many other ways to gather our personal data.

Doug Sharp, Oath’s vice president of data, measurements and insights, told the Wall Street Journal that email scanning is an effective method for improving ad targeting. “He said that the practice applies only to commercial emails in people’s accounts—from retailers, say, or mass mailings—and that users have the ability to opt out,” the WSJ wrote.

“Email is an expensive system. I think it’s reasonable and ethical to expect the value exchange, if you’ve got this mail service and there is advertising going on,” Sharp said.

“Yahoo paid $4 million in 2016 to settle a federal class-action lawsuit that claimed its scanning of email violated federal wiretap laws,” the WSJ noted. “Yahoo, which didn’t admit wrongdoing, agreed as part of the settlement terms to make a technical change: Rather than scanning emails while they are ‘in transit,’ Yahoo now waits until they arrive in an inbox to scan them.”

In their pitch for new business, Verizon explained to the advertising community that they put users in categories based on what they learn from reading receipts, order confirmations, and other material found in the email.

For example, flight confirmation emails put us into the Yahoo audience of frequent travelers. Brokerage trade confirmations put us into the Yahoo audience of investors. Auto loan notifications put us into their audience of car owners, and ride-sharing driver emails mean the individuals are self-employed. People can be in multiple categories.

Verizon’s email scanning then goes even further than what Google used to do. Yahoo creates these “interest profiles” of their users based on what they detect in the email and then uses that data to follow the users across the web and serve up advertisements on other sites.