Company Emails Setup. Help!

My friend asked me to setup a bunch of email accounts for his small company on his hostgator hosting account. For workers and volunteers. And he wants to have an access to all email accounts and to prevent the workers from changing passwords.

Please, help me with an advice on how to do it in an efficient way. Default email setup at hostgator in my knowledge allows everyone to change their passwords.

Is there a workaround or I need to look for totally new setup, with different email softwares.

How other big companies with hundreds of workers manage their email account assignments?