I would love to be able to hit the spacebar to scroll down the message in the preview pane.
I rarely open up an email message in a new window: Outlook follows this convention - browsers do the same thing too.
It’s immensely convenient - it’s impossible to miss the spacebar, no need to position the cursor on the scrollbar - please consider adding to the next version!
I would like the message preview to scroll on spacebar even when it is not focused (eg: message list is focussed). Outlook does this and it’s great when working through a long list of messages.