How to open a Hangout Chat from Gmail
Have you made a new contact over email? Quickly add them to Hangouts Chat instantly
Take a more professional form of communication with a Hangout Chat.
Open the email in Gmail and hover over the name of the sender.
Then click the Hangouts Chat or Video option. If this is greyed out, Gmail has detected the sender does not have a Google account and the Hangouts Chat option is automatically disabled.