On Thursday Google announced this change.And this change is related to privacy so it causes some privacy advocates.However,a user email address won’t be visible till one chooses to respond to the email sent via Google Plus.Google also explained that, mail send like this will land in your social category and are not in the main inbox.Google also give all control of this feature in your hand,by using this feature you can choose who can email you via your Google plus profile.Their is four option 1) Anyone on Google + 2) Extended circles 3) circles 4) No one. from this list you can choose as your wish. by choosing they allow to send you email on Gmail.Google did this change to make more strong integrate between Google Plus and Gmail.
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Update: Google+ is only available for G Suite accounts through work or school. Consumer accounts (typically ending in @gmail.com) were shut down on April 2nd, 2019