You are wasting space!
No, the new look sucks because you have put a fuckton of extra space in the left-side bar. We could be viewing twice as many folders, but no, you had to "fix" it.
We don't all have the cutting-edge giant computer monitors like your developers probably do. Test it on a normal screen, duh!
Jack Shipe commented
Improve the use of white space (e.g., compress content within one screen). The UI approach should be less physical effort to view more information (i.e., smarter, not prettier).
Dr P A Bamber commented
Offer compact, standard and 'for stupid people' space options.
The Borders and icon pick boxes, need to be thinner and combined into one row.
I don't need to see the tab "INBOX" when it is already highlighted in the folder list. Move the Search box to another area. AND you gain a whole row of real-estate, for READING, email!
The filter pull down can be combined with the up "Next".
The "Office 365" banner/ribbon/wallpaper section could be half as thick and still function. And then provide more screen space to read the emails.
If I wanted something designed by Fisher Price, I know where to find them.