It's a nice idea but I think it would be a little too burdensome for every single email. Maybe if the mail was going out to >N people where N is configurable by

It's a nice idea but I think it would be a little too burdensome for every single email. Maybe if the mail was going out to >N people where N is configurable by the organization. I think one of the reasons why no one's ever done this is that with traditional email, it's impossible for the sender to know how many people one email has reached, or will reach. But I think Threadable (recent YC startup) could actually do this.