You may have noticed that other Google+ users can send you emails on Gmail, even if they don't know the email addresses.
To prevent this from happening, follow the below procedure:
- Connect to your Gmail account.
- Go to Settings > General.
- Scroll to the "Email via Google+:" section.
- Next to "Who can email you via your Google+ profile?" select "No one".
- Scroll down to the bottom of the page and click on "Save Changes".