Earlier quoted context omitted.
I don't follow. Are you saying that BigCorp would demand key escrow? They already deploy custom email solutions today so I don't see the issue.
I am saying you can't keep the keys just on a stick in the employee's pocket since multiple people need to have access to the data. And if those keys are stored by a company subject to US jurisdiction, we're back to the same problem.
Key escrow is the usual solution to an employer needing access to employee materials.