Microsoft
I agree with both Sam_T and DavidYorkshire.
I'd add, organization typically budget for needs 1 year+ in advance. When I went to budget for the next non-released version of Exchange believe me leadership was far from thrilled. We have ~200,000 mailboxes between On Prem and EXO, we use On Prem servers to support mail flow, mailboxes that would not "fit" in EXO and other services that EXO does not offer/support or are cost prohibitive to do so. Like others have said moving them, changing them, changing processes for them with no runway is simple untenable. From a security standpoint my guess is some will be running on out-of-date Exchange which can't be the intended goal. Please give us direction so we can plan.
