Email has nothing to do with calendars. It happened that people in offices used email and attended to a lot of meetings. Microsoft built a client/server system

Email has nothing to do with calendars. It happened that people in offices used email and attended to a lot of meetings. Microsoft built a client/server system (Exchange) that managed both email and calendars. There were probably previous systems like that, I don't remember. We need only a calendar client now (usually on phones) even if most systems send an email notification.