> Is "reading an email" one thing? And "writing an email" another thing? What about "spellchecking the email"? What about "managing all my email contacts"? What about "back up my emails"? What about "sign email with GPG"?
>
> Do all of these things really need a separate program?
Yup. I used it for a few years. It also had a Tk-based GUI. Every email message is a single file. "Folders" are directories. So you can use your usual text-processing commandline stuff: grep, sed, awk, etc.
Using MIME or GPG required a little configuration (mostly preset properly) which hooked external programs to preprocess before sending or displaying the message.
There was a suite of programs that worked that way: https://en.wikipedia.org/wiki/MH_Message_Handling_System