Delayed E-mail Sending: Another Obvious-in-Hindsight simple but excellent idea
The trick is, the sending of the e-mail is delayed a few seconds after you click “Send”, allowing you the chance to change your mind before the e-mail is really sent.
It’s a great idea, although I think the delay could be even greater. I could tolerate that an e-mail is only sent some 30 seconds or so after I think it has been sent. This gives me a good window of time to undo.