The interesting thing about this is that it affects people who have never been to the US and never intend to go, or those who do but take 'precautions' to protect their privacy (secondary devices, double encryption etc) as most of the data in anyone's inbox is not generated by them.
It also affects U.S. citizens who don’t even have a valid passport and no intention to leave the country. According to the CBP being in the extended border zone is enough to be crossing a border and therefore be subject to a warrantless search.
That's pretty scary.