We've all been in this situation before: You hit "send" on an email, then wish you could take it back. Maybe you typed someone's name wrong or entered the wrong email address. With the newly updated Gmail app — the first real overhaul in four years — for iOS, you can now retract the email before it really goes out. The "Undo Send" button for mobile comes more than a year after Google graduated the same feature for desktop from beta to an official setting.