Have a look at my notes on an older thread https://discourse.mailinabox.email/t/raspberry-pi-setup/6395
Not all required libraries are installed, you will need to: sudo apt install libffi-dev
Also, after running on a Pi for a while, I changed to a more stable platform. See https://discourse.mailinabox.email/t/running-from-home/6459/12?u=andrew