Earlier quoted context omitted.
> Not everyone has a 16:9 monitor, so super wide views don’t work for me. I'd say that you're in a small enough minority that most people will design right past you, just like most websites have an acceptable minimum percentage of browser feature availability after which you can make that feature a requirement for functionality. Especially as screens tend to get wider, not thinner.
I see what you're saying, but wouldn't it be also great if there was a mail app that didn't consume the entire screen real estate.
If you want something really small, perhaps mutt in a terminal could work. :)