Or you were much too angry when you wrote it. For Gmail users there has been a quiet and until-now-unadvertised fix for this, known as the “Undo Send” feature.
The feature does exactly what its name implies: it lets you un-send an email for a short while after sending.
Of course, it isn’t reaching out and snatching the email back — it just holds the email for a brief period sufficient for you to evaluate your regrets — but it can still be a life-saver. More