Thank you for fixing the broken image links. I have been also looking for this. One thing I'm unsure of, it the guide up to date? The original thread is bit old. Is there any smartphone guide available? Many doesn't have any desktop devices.
All of the software mentioned in this article should work with the latest operating systems, and last time I checked, they had the exact same user interfaces as seen in this guide. So it should still work right now.
There are some smartphone apps that can import your PGP key and encrypt messages with it, although I do not believe any of these have integrations with email. But it's simple enough if you're just sending text content without attachments.