This should be the mail address of the user in the source AD or AAD provider. Example: Jamal.Hartnett@contoso.com Team Services will communicate with the source provider to fill all other fields on creation.
OptionalstorageOptional: If provided, we will use this identifier for the storage key of the created user
Use this type to create a new user using the mail address as a reference to an existing user from an external AD or AAD backed provider. This is the subset of GraphUser fields required for creation of a GraphUser for the AD and AAD use case when looking up the user by its mail address in the backing provider.