This is one reasone that keeps me on Apple's Mail.app: open multiple windows for different mailboxes / folders / smart mailboxes and drag & drop at will between

This is one reasone that keeps me on Apple's Mail.app: open multiple windows for different mailboxes / folders / smart mailboxes and drag & drop at will between them. Keep a window for specific smart folders if there are special keywords / people you want to give priority. Tuck it in a corner of the screen without taking up lots of realestate. To be fair, Apple really screwed that workflow in 10.15 by disallowing customization of columns like they used to have since 10.0. But still, the multi-window organization is so much more flexible than the all-in-one-window setup. (For those concerned with tidiness, a window manager takes care of that problem.)