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All Atlassian accounts with email addresses from verified domains become managed accounts.
What can they do?
they can get all benefits of Atlassian Access,for example they can do SSO & 2-factor Authentication.
Ref
https://support.atlassian.com/user-management/docs/what-are-managed-accounts/
https://support.atlassian.com/user-management/docs/verify-a-domain-to-manage-accounts/