Ever wanted to email someone you know, but haven't yet exchanged email addresses? Starting this week, when you're composing a new email, Gmail will suggest your Google+ connections as recipients, even if you haven't exchanged email addresses yet.
How it works with email addresses Emailing Google+ connections works a bit differently to protect the privacy of email addresses. Your email address isn't visible to your Google+ connections until you send them an email, and their email addresses are not visible to you until they respond.
Receiving email from people outside your circles If you receive an email from someone outside your circles, it will be filtered into the Social category of the inbox (if enabled) and only after you respond or add them to your circles, can they start another conversation with you.
How to control who can contact you You're in control of whether people can reach you with a new setting in Gmail on the desktop. To learn more, check out the Help Center.