There are use cases where an Atlassian cloud site caters to both internal and external users for an organization. At the moment, Atlassian Access allows to enforce security features to domain users that they own but not to external users that are identified by an email address under a domain that is not their own. Still, log-in security is vital for those type of users.

Suggestion :
Provide the ability for site owners to enforce security features on their external users.