The first update to the terms and conditions since November 2013 warns that any information users submit to and share with Google systems can be analysed.
The terms and conditions already stated that any information uploaded, sent or stored via Google services gave the firm a worldwide licence to "use, host, store, reproduce, modify, create derivative works, communicate, publish, publicly perform, publicly display and distribute such content".
The new addition to Google's privacy terms suggests that this reach is extending further. "Our automated systems analyse your content (including emails) to provide you personally relevant product features, such as customised search results, tailored advertising, and spam and malware detection," it said. "This analysis occurs as the content is sent, received, and when it is stored."
Google said that the changes are clarifying, rather than changing the terms. "We want our policies to be simple and easy for users to understand. These changes will give people even greater clarity and are based on feedback we've received over the last few months," it said in a statement.
The changes have sparked controversy, with the bulk of responses coming from users who are worried that Google is now able to read their emails and scan them for purposes such as targeted advertising. Google is so far unapologetic about the changes.
This matches the view Google put out in August 2013, when it said its users should not expect any privacy protection.
At the time, Consumer Watchdog Privacy Project director John Simpson advised anyone who wanted privacy to look elsewhere for email services.
"Google has finally admitted they don't respect privacy. People should take them at their word; if you care about your email correspondents' privacy don't use Gmail," he said.