Your email address is different than your username and cannot be used as the username to sign in to your email account. View your email address at https://myaccount.microsoft.com
If you are unable to log in 24 hours after registering for courses, try resetting your StarID password on the StarID Self-Service site. It can take some time for the password to sync from StarID Self-Service site to the Microsoft login page. Email passwords cannot be changed on the Microsoft login page.