I agree with your point, but I don't accept the premise that people are responding quickly to emails. 99% of emails are transactional these days, and places whe

I agree with your point, but I don't accept the premise that people are responding quickly to emails. 99% of emails are transactional these days, and places where they aren't (eg. internal at BigCorp) it's not unusual for people to be receiving 1000s a day. Replying the same day is considered quick for places with C level.