You don't necessarily need Outlook installed but you do need MAPI installed. So if Outlook is not installed you would have to probably install the server side MAPI. I've done that on services and other applications where it's
not appropriate to have Outlook installed.
RDO will log into a MAPI session or start one if necessary. That would mean some MAPI profile has to be accessible for use or it has to be created dynamically.
Different mail formats are supported by RDOMail objects and the editors they expose.