Google has tweaked Gmail so that anyone who can find you on Google+ can send you an email, even if they don't have your email address. If you don't fancy being spammed by the wider Google+ community, there's a setting to switch the option off.
Google is rolling out the new Google+ option to all Gmail users over the next few days; you'll receive an email when it's active on your account. Once that happens, suggestions for email addresses will be drawn from your Google+ connections as well as your email contacts.
Google's announcement emphasises that this won't necessarily impact your privacy: anyone who emails you via Google+ but who isn't in your circles will be automatically filed in your Gmail Social folder, and won't be able to message you again unless you respond or add them to one of your circles.
If you don't want email from Google+ connections at all, you can turn the option off in Settings, under 'Who can email you via your Google+ profile?' The default setting is 'Anyone on Google+', but you can switch it to 'No one' and cut down on Google-approved spam in your inbox.
Google is persisting with its Google+ strategy, and it's becoming harder and harder to avoid exposure to Google+ when using Google services. Check out our guide to stopping Google+ from taking over all your apps, but remember: the price you pay for free services is that the providers can do what they like with them.
Reach the people you know more easily [Official Gmail Blog]