When you go in to create an account and receive "the provided email address contains a reserved domain name."

This means your company has enabled Federated Login making it easier for you to access the system without needing another password. 

Additional Details here: https://www.mongodb.com/docs/atlas/security/federated-authentication/).

To log in, please visit our sign-in page, enter your email address as your username, and click NEXT. You will be directed to your company's SSO login page, and an account in MongoDB University will be created after the SSO login is completed. You will then be part of a cloud-federated domain and follow your company login flow from here on.

Please reach out to learn@mongodb.com if you have any additional issues.