Thanks Greg.
I guess my underlying (and unstated) thread was that the implementation of the mail protocols used in MSFT's cornerstone device-based products - MAPI over HTTP (for desktop Outlook) and EAS (for everything else) - would appear to be different from the Graph API implementation that MSFT wishes developers to use.
This not a criticism; I am just trying to understand MSFT's development direction and in particular whether the implementation of MAPI over HTTP and of EAS is intended at some date to use the Graph API instead.
MSFT has - correctly in my view - been progressively removing 'non-standard' implementations, e.g. the massive conversion of hotmail, live and outlook.com from a custom back-end to Exchange Online.