Edit/Solved: Thank you for all the great input! Both on alternative solutions and on security implications. I'm going to make a draft on how I would setup the e-mail method as securely as possible as a programming/scripting exercise, but will IRL probably end up using either some reverse tunnel/shell variant.

Edit 2: or, as a hardware solution, install an extra NIC that I expose to the opennet - thus enabling remote port forwarding - while binding all my sensitive processes/traffic to my encrypted NIC.

I cannot ssh into my Linux box from outside of my LAN since I'm behind a VPN that doesn't support port forwarding. Is it possible to make my Linux box receive, interpret and execute commands through e-mail instead? I've tried looking for answers through DuckDuckGo's search engine, to no avail. If I may dream, I would like to setup an e-mail server with a systemd service or just run a script that continuously downloads the emails, prints their content to stdin and executes, perhaps through command substitution, whatever is in stdin.