I've been a software engineer for over 30 years, and have been using Linux almost exclusively for about eight years. I was a Lavabit customer. After Lavabit was forced to close, I undertook the challenge of installing my own mail server, with IMAP access, and basic spam detection using DSPAM. I am not exaggerating when I say that it was one of the most involved and complicated processes that I ever tried. A major problem is that in addition to installing all of the software, you have to do so in such a way that all of the communications and storage are secure. I eventually succeeded, mostly, I'm still having weird problems with my DSPAM detection. It took almost a month to set up and work out all of the bugs.
Before Lavabit, I was a customer of https://countermail.com, based in Sweden, and they are just about the only real alternative that I would recommend at the moment. They appear to do encryption "right", and offer all of the features, including web access, that most customers will want.