I frequently receive a notification from my 'phone and recognize the sound as a new email on the Gmail app and many times I'm at work, etc, so I switch to my open Gmail tab. Sometimes I even wait a little bit before going to the Gmail tab. And it's not there. I usually keep my hands on the keyboard.
Checking new mail is one of the few times during the day that I have to move my hand to the mouse for a one-time action just to immediately go back to the keyboard. I got fed up because I couldn't find it on Google's list of Gmail shortcuts and started searching around. Maybe no one has ever asked the question or just no one cares.