One company told the Wall Street Journal that the practice was "common" and a "dirty secret".
Google allows users to connect third-party services to their accounts, and it's here the problems arise. Some companies may request access to "read, send, delete, and manage your email" which gives them full access to emails on Gmail.
But the Journal found that Google "continues to let hundreds of outside software developers scan the inboxes of millions of Gmail users who signed up for email-based services offering shopping price comparisons, automated travel-itinerary planners or other tools".
While several app developers have termed this a "common practice" where humans access user data to develop machine algorithms, Google is yet to ensure that user data will not be compromised in a Facebook-Cambridge Analytica manner. Its rules also bar app developers from making permanent copies of user data and storing them in a database.
According to the Wall Street Journal, this permission sometimes allows employees of third-party apps to read users' emails.More news: Durant opts out as free agency looms
Some of these companies train software to scan the email, while others enable their workers to pore over private messages, the report says.
Google, however, has denied privacy violations, stating data is provided to vetted third-party developers only and with the users' explicit consent. "Return Path is an app that collects data for marketers by analysing users" inbox emails.
Now You: Do you permit third-party apps access to important data? This is in contrast with what Google promised a year ago, where it said that it would stop reading its users email messages, which might be true, but it has done very little to stop other partner organisations from doing so. The company recently rolled out new features for Gmail in a bid to make it easier for users to navigate their account and review security and privacy options. A Microsoft spokesperson said developers were not allowed to access customer data without consent.
Google said a year ago it would stop its computers from scanning the inboxes of Gmail users for information to personalize advertisements, saying it wanted users to "remain confident that Google will keep privacy and security paramount".