Hangouts, since the beginning, has separated incoming messages into two categories. Either the app detects that you probably know the person that’s contacting you (by way of you circling them, them having your email address, or otherwise) and lets them send you a message directly, or it puts incoming messages into an “Invitation” that you have to accept. How this works has never been customizable, but now Google is letting you customize these invitations to make them more or less strict.
Here’s the image that Jordanna Chord shared:
In the new options, you can choose to go with Google’s recommended system, or you can opt to customize three different categories of incoming messages yourself. If you’d like, you can require that only invitations can be sent — regardless of if the sender has your email/phone number or not. Or, if you’re more of a free spirit, you can conversely use this opportunity to open up your inbox to any and all messages and allow everyone to contact you directly. Personally, I like the way Google has things set up. But I also like options. Options are good.
These settings will be available across the Hangouts apps, and of course, those who are using the Hangouts app on the desk through Google+ or otherwise will be able to take advantage of them as well.