A letter from Google to lawmakers revealed that third-party app developers can access Gmail users' messages for ad targeting purposes -- as well as share the data with partners.
Verizon-owned Oath is pitching a service to advertisers analyzing AOL and Yahoo emails to provide targeted ad data, according to The Wall Street Journal.
The outside app companies receive access to messages from Gmail users who signed up for things like price-comparison services or automated travel-itinerary planners.
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