Google has defended its policies blatantly by saying: "Developers may share data with third parties so long as they are transparent with the users about how they are using the data". Some app companies even have the ability to read the contents of your emails and share that information freely, but Google says it makes sure these companies first disclose to users how they're using the data.
The revelation prompted concerns about whether Google is adequately monitoring misuse of Gmail user data to ensure its users aren't exposed in the same way Facebook's lack of developer oversight allowed political consultancy Cambridge Analytica to acquire millions of Facebook users' data through a third-party app developer.
Google said in a letter to USA senators made public on Thursday that it relies on automated scans and reports from security researchers to monitor add-ons after launch, but did not respond to lawmakers' request to say how many have been caught violating the company's policies.
The senators asked whether Google was aware of "any instances of an app developer sharing Gmail user data with a third party for any purpose".
Gmail-integrated apps provide a variety of benefits to users, from assisting them in getting refunds after a product's price drops online to helping them craft basic email replies.
Now, privacy officials from Google, Apple and Amazon are preparing to travel to Capitol Hill next week, for a Commerce Committee hearing.
Google itself has mined users' emails since Gmail was launched in 2004, but announced past year that it would stop the practice, amid privacy concerns and a federal wiretapping lawsuit.
Who's reading your Gmail? Google claimed that it vetted these services.
Gmail's not entirely confidential "confidential mode" expiry-date email feature is now available on mobile apps.