I like the layout of Windows 10 Mail - the built-in mail app.
I'm looking for a client organised in the same way - The accounts on the left, the mail in the middle and the reading pane on the right.
I like only seeing the folders for the account I've selected.
A dark mode is nice but non-essential.
I'd like this program to run on Windows, Mac and Ubuntu.
Nylas N1 is the extensible, open source mail app.
It has a Dark Mode built in, a "Two Panel" layout and is extensible. It runs on Windows, OS X, Linux (.deb and .rpm) available.
The messages are shown tall in the middle panel - not just one line - when you shrink that section.
There is an open feature request to only show the folders of the current mailbox, and a plugin would probably be possible to achieve this functionality.
You could try Thunderbird in the "Vertical View" Mode - I have mine set to a dark theme but there are lots available.
