Well now you can if you use gmail. Gmail gives you up to 30 seconds to unsend that email you wrote to your boss telling him how you really feel.
Since you never know when you’re going to need this feature, drop everything now and go change your settings:
In Gmail, click the gear in the upper right corner below your profile picture to access Settings.
Under the General tab, check the box next to “Enable Undo Send” and use the dropdown to customize your cancellation period to 5, 10, 20, or 30 seconds.