If you happen to send an email to one of the 400 million people who use Google's Gmail service, you shouldn't have any expectation of privacy, according to a court briefing obtained by the Consumer Watchdog website.
In a motion filed last month by Google to have a class action complaint dismissed, Google's lawyers reference a 1979 ruling, holding that people who turn over information to third parties shouldn't expect that information to remain private.
Source: https://www.businessinsider.com/gmail-privacy-google-court-brief-2013-8