Not sure why these people are spending so much money to develop their own hardware (40% of total cost) when this software (mail server, PGP) can be run on many cheap, off-the-shelf systems, like Raspberry Pi.
Raspberry Pi is bigger and less energy efficient.
On top of that, we don't use it for prices reasons, people have already tried to sell all-in-the-box devices based on Raspberry Pi and the end up being expensive.
https://www.kickstarter.com/projects/1547898916/own-mailbox-...