Google has added a new feature to its Gmail service, which could allow strangers to send mail to even unknown users, raising privacy concerns among users.

The new feature integrates users’ existing contacts as well as email addresses from their Google+ social network account, allowing them to send emails directly to friends, and strangers, whoever use Google+.

Some privacy advocates are of opinion that Google should make it as "opt-in feature while ,Electronic Privacy Information Center executive director Marc Rotenberg was quoted by Reuters as saying that the new feature "troubling."

Google product manager David Nachum said: "As an extension of some earlier improvements that keep Gmail contacts automatically up to date using Google+, Gmail will suggest your Google+ connections as recipients when you are composing a new email."

"Your email address isn’t visible to a Google+ connection unless you send that person an email, and likewise, that person’s email address isn’t visible to you unless they send you an email," Nachum said.

Users not willing to receive email emails from other people on Google+ are allowed to change their settings so that they get messages only from people added to their networks of friends or from nobody at all, the company added.

Google, however, assured that the new feature would not disclose email IDs of any Google+ users to strangers, as emails from unfamiliar users on Google+ will be directed to a special section within the receiver’s mailbox.

Google+ users will be notified via mails during the next two days about the changes and assisting them in changing their settings.