Didn't notice that. Does that mean you can take back a sent email? There have been times I sent emails by mistake and this feature will surely be helpful if it works the way it sounds to be.
You can undo email just right after you sent the email . when you leave that page or refresh then you can't take back your email . You can enable it in settings. see attach image. Click the gear in the top right . Select Settings. Scroll down to "Undo Send" and click Enable.