In the previous UI two actions that I use a lot (star and mark as read) were very conveniently towards the beginning of the email list and their respective buttons (the empty/full star and the little blue dot) were always present on the screen so I would directly point at them to click.

Now there are two UI downgrades:
1. the actions are now hidden until I hover on that email - which means I first need to hover, then observe where the little actions box show up, locate the icons I want, point and click; previously the buttons were always visible which means you could directly point in their direction
2. the actions box is now moved to the right which is well away from the visual focus area which is naturally to the left. On a desktop browser where one usually has a big display, those actions are far far away to the right, meaning there is considerable mouse travel until one reaches that area.

Even moving the actions to the left, before the subject column would fix a lot of these usability issues. Star and mark as read I think are very commonly used actions (I'm sure you have the telemetry to prove it) so they would not take that much space. The other actions -> move (usually easier to drag and drop, also not sure how much people bother to use folders and constantly move emails - easier to create automated rules for that) and delete (easy to press the DEL key) are probably not so used actions and can remain to the right