> The reason email doesn't support unsending is not some essential property of messaging. It's just that at the time our email protocol was defined, email supp

> The reason email doesn't support unsending is not some essential property of messaging. It's just that at the time our email protocol was defined, email supports unsending in exactly the same ways you described for packages. It most definitely is a property of messaging. Your fron porch is called "outbox". works the same - you can delete from outbox before sending. If both you and your recipient are on a properly configured Microsoft Exchange server, you can unsend a message, which is similar to the university department. And if you aren't, you can still send a message saying "hey, please don't open the last email", and it's up to the other side if they do or don't. For better and worse, email has a lot of similarity to real mail, down to the distinction between content and envelope. The main difference is the speed of delivery - you would not expect any of the ways you suggested to work 3 months after you've sent your package -- and yet, compared to the 500ms or so that it takes the email to reach the recipient, that's what attempting to unsend after one minute is.