> The only sane alternative that I can see is to run your own server, on your own hardware, preferably hosted inside your own home for maximum legal protection. Of course, unless you really know your stuff then your data could well be at greater risk from both legal and illegal intercept.

This is what I do. At home I have a Chromebox with FreeBSD and a fully encrypted disk. I have a VPS with an OpenVPN server and the required ports are forwarded to my own box. IMAP and SMTP submission require TLS so those are fully covered. Like you said though, the only thing you can't reasonably forcibly encrypt is SMTP itself. Most of the mail I receive comes with STARTTLS but not all.

With this setup the VPS provider can't see anything when SMTP happens with STARTTLS. Obviously if they really want to read my mail they can start MITM'ing the STARTTLS away because it isn't forced but this is the best setup that's reasonable.

My ISP for my home can only see encrypted OpenVPN traffic too. In fact the VPS is in another country but that's only a consequence of the silly VPS prices in my country.

Obviously with this setup I don't have to surrender my private key to anyone either, it sits on my own box (and I use a legitimate CA-issued certificate).