When we import a role into a group, everyone gets a 'You are now a member of [GROUP]' email. How do I turn that off? We are working on live website and it is very embarrassing for us if our thousands of users gets an email while we are setting up new groups and testing them. I would highly appreciate if you could help us.

You can stop the emails by entering a different address in the host SMTP settings while you import roles. You could use a localhost server like papercut to catch the emails.