While I obviously still use email, the company I work for doesn't use it. We only use slack (and various other communication tools like Github and Monday).

We use our personal emails to set up the accounts. It's an interesting experiment that seems to be working fine so far. Not sure how it will work as we continue to grow (only about 40 employees right now.)

> We use our personal emails to set up the accounts.

I would object to that. Personal and business don't mix.

Likely, there are people that have never used email either.

Well, there are no people who have used Slack who have never used email, because you need email to sign up for Slack.