I can't switch back to the classic UI view. Please add this option back, I completely dislike the new design.
If you "must" keep the new UI as it has been rewritten, please add a theme to look as close if not exactly as the old one.
The new design has everything enlarged so that I get less done on a page.
For me, the mail UI is a tool and with the new look you made it a Swarovsky: very fancy with greatly reduced UX mobility.
I have started exploring other available market options.