If you have installed Easy365Manager to a system where Internet Explorer was never used to log in to Office 365, you may see a warning in your browser:
To allow the Microsoft Modern Authentication process, Internet Explorer must be allowed to run scripts for the Internet zone. Configure it in Settings in Internet Explorer:
This change only needs to happen one time.
When this is configured, you can authenticate with Office 365 and Exchange Online. Once you have completed the authentication, you can reset these security settings if you like.