If you want to learn more, then you will need to move away from casa. Casa is pretty much just a collection of custom docker images that play well together and with their interface. You could grab an old computer, install Linux, and do more but you would expend more time and effort.
I had a hell of a time trying to use Gmail and exchange email from the terminal clients I tried. Mostly because of security features. I never got it working but aerc looked really nice.