Judicial Mandate: Necessary or Superfluous?
Yes, there may be a distinction between private and company emails. But it seems like the lines are somewhat blurry, here.
Imagine if Ford motors said: Oh, we can look into the Ford cars that Ford employees have bought with their own money and drive to weekend outings with their families, because we made and service the cars.
I don't think this will fly very far.
Should webmail and similar services be regulated so as to put the interests of consumers ahead of service providers? Perhaps, and in many ways this is the approach taken by European regulators in many industries. On the other hand, it has been argued that the rather onerous data protection regulations in the EU are partly to blame for the lesser competitiveness of European firms in that marketplace, by imposing overly burdensome regulatory regimes on entrepreneurs and thus making the barriers to marketplace entry far higher than in the US.
Microsoft has no legal authority to make that call.