A new Gmail feature that would let its users receive messages from people they don't know is raising concerns among some privacy advocates, according to a Reuters report.

The new feature, which Google had announced last Thursday, is said to broaden Gmail users' contact list. It would include email addresses of their existing contracts and names of people on Google+. This means that anyone can send another an email directly via Google+.

Google moves to integrate its Google+ with its other devices such as Gmail. For example, when a new user signs up for Gmail, the user will automatically be given a Google+ account. Google said that the integration will make it easier for people who use both services to communicate with others, especially their friends.

"Have you ever started typing an email to someone only to realize halfway through the draft that you haven't actually exchanged email addresses?" according to a company blog post when it announced the new feature. "You're in luck, because now it's easier for people using Gmail and Google+ to connect over email."

However, some privacy advocates said that Google should have made the new feature an opt-in process in which users should explicitly agree to receive messages only from people who are part of their networks.

Marc Rotenberg, executive director of Electronic Privacy Information Center, a nonprofit organization, called the Google's new feature "troubling."

"There is a strong echo of the Google Buzz snafu," Rotenberg said, referring to a controversial social networking service Google launched in 2010. Google Buzz features used the contact list of Gmail users' to create social networks available for the rest of the world to see. It led to an uproar and ultimately a settlement with the U.S. Federal Trade Commission.

But Google said the new feature would not expose users who are using Google+ and their email addresses to strangers. Instead, emails from strangers on Google+ will be routed to a special section within the recipients' mailbox separate from messages from friends and other contacts.