In simpler terms, you are exposed to everyone on the internet and they can send you unwanted mails whenever they want. The only caveat is that you have to be on Google+. We have been trying to resist these aggressive measures by Google to push G+ with our own ways, but this Gmail integration is critical breach of privacy. This Gmail integration feature is set on default to “Anyone”, so anyone from Google+ can contact you. To stop random people contacting you, follow these steps:

  1. Login to Gmail, Go to Settings.
  2. Under General settings, search for “Email via Google+”.
  3. Select your choice of audience from the drop down – Anyone on Google+ : Your email is public and anyone can send you emails – Extended Circles: You can receive emails from friends of friends in your circles – Circles: Only from people in your circles – No one: If you do not want to receive mails from anyone through Google+
  4. Now scroll to the bottom and select Save Changes.

Drop selection choices are in reverse order of your privacy.  Select the one that suits you. I am going for only circles, that is, from my friends I know.

Stop Mails from Google  Users to Your Gmail - 64