Most executives I've known use a web portal for sensitive emails and communicating with one another. Usually these portals have something like "Secure Email" i

Most executives I've known use a web portal for sensitive emails and communicating with one another. Usually these portals have something like "Secure Email" in the name, but they are really just a web interface to email that limits what can go to whom, has data retention policies and usually multi-factor authentication. Courts can get the emails from these providers assuming the provider is legit and law abiding and reside in a country where law enforcement have jurisdiction. Some are not. The executives can be compelled to turn over authentication.