Google's lawyers have said that Gmail customers have "no legitimate expectation of privacy", in a staggering statement contained in a court briefing.
Referencing a landmark 1979 privacy case, Google argues that users should not expect privacy when they have voluntarily processed their communications through the company.
The statement was made in a motion to have a class action complaint against the firm dismissed. The complaint argues that Google violates federal and state wiretap laws when the company scans emails to determine what ads to show the user based on message content.
"Just as a sender of a letter to a business colleague cannot be surprised that the recipient's assistant opens the letter, people who use web-based email today cannot be surprised if their emails are processed by the recipient's [email provider] in the course of delivery," Google's brief says.
"Indeed, 'a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties,'" it adds, quoting the 1979 Smith v. Maryland case.
In response to the statement, the American Consumer Watchdog group has urged people "who care about their email correspondents' privacy" to not use the service.
"Google has finally admitted they don't respect privacy," said John M. Simpson, Consumer Watchdog's Privacy Project director.
"Google's brief uses a wrong-headed analogy; sending an email is like giving a letter to the Post Office. I expect the Post Office to deliver the letter based on the address written on the envelope. I don't expect the mail carrier to open my letter and read it.
"Similarly when I send an email, I expect it to be delivered to the intended recipient with a Gmail account based on the email address; why would I expect its content will be intercepted by Google and read?"
It is not clear if the case is linked to Microsoft's anti Gmail 'Scroogled' campaign.