OpenSMTPd is simple enough to setup on your own. No need for gigantic ‘dockerized’ email packages where it is virtually impossible to understand what is going on.
But i want imap too, and a web-mail, oh and a Calendar and contact (with team-functionality) too, synchronize them to my phone, and i want sieve functionality, anti-spam, and because it's written a pseudo antivirus-solution. And a self-service solution so users can reset the password with 2FA...still easy?
So you give your users the root password so they can change the password them-self....oversimplification often solves just a small portion of a bigger problem.