🚨 2020 Update: I recommend using mkcert to generate local certificates. You can do everything below by just running the commands brew install mkcert and mkcert -install. Keep it simple!

This gives you that beautiful green lock in Chrome. I'm assuming you're putting your SSL documents in /etc/ssl, but you can put them anywhere and replace the references in the following commands. Tested successfully on Mac OS Sierra and High Sierra.

sudo nano /etc/ssl/localhost/localhost.conf

This note describes how to set up the Mutt or NeoMutt email client to work for Gmail and GnuPG, for two Gmail accounts. The method can be trivially extended to more than two accounts. The configuration should work for both macOS and Linux.