Do you have MySQL server running before installing iRedMail? Do you set a password for MySQL root user?
Here's my suggestion: iRedMail is designed to be deployed on a FRESH server, so you'd better install a minimal server to install iRedMail.
Also, next time you install iRedMail, try using below command instead of "bash iRedMail.sh", it will print addition details on terminal, please paste it here to help troubleshoot if it failed again.
# IREDMAIL_DEBUG='YES' bash iRedMail.sh
It's a completely fresh VM. I don't "believe" it has anything installed. But as I said I'll double check.
I certainly haven't set any mysql root password and can confirm that once the iRedMail install has completed
the mysql root password is set to what I entered during the iRedMail install. So I don't think the install is
failing to connect due to a password issue.
I'll try that extra debug option too.