At least one system administrator with manager rights needs to be set up in the ACL. The System Administrator access is required e.g. for updating the application design.
System Administrators need to have "Manager" level access with the attributes "Create documents", "Delete documents" turned on and the role [Administration] assigned to them.
Manager access with the credentials "Create documents", "Delete documents" and the roles [Administration] and [EmailEditor].
Among other things, the role [EmailEditor] is required to assign the editing permission to the email in the Outbox in the configuration.