GMail kinda has it. If you look in GMail Labs, you'll see the option to delay sending an e-mail by 1 minute. That gives you 1 minute to change your mind. I w

GMail kinda has it. If you look in GMail Labs, you'll see the option to delay sending an e-mail by 1 minute. That gives you 1 minute to change your mind. I wish more mail clients had this feature.