Once initially turned on and configured, the File Storage service is available for use by all Helm users. The Files service is a global service controlled by the Helm primary user and must be turned on by the primary user for others to use it.
The Files service is also connected to the primary domain of the Helm, not secondary domains. That said, any user of any Helm domain (primary or secondary) can take advantage of these services.
Users can log in using any Helm email address. When sharing a file link to other people, the domain displayed in the link will be the primary email domain.