I just came across this project: https://github.com/scintill/gpg-mailgate
does encryption of all incomming emails with gpg. There is web interface for key upload and seems like it was a relativelly complete package for e2ee of emails at rest. However seems like not really being user or worked on for years. There is some forks here and there though. Anyone familiar with it? Or perhaps there is something more up to date and working that I have missed.
I did first successful test and seems like thing just works (didnt test the web interface).