I’d like to have the option to remove the “Today”, “Last Week”, “Older” separators. For me, they just use up screen space while not providing any useful information.
Secondly, I’d like the option to remove the quick search box at the top of the email list. Here again, removing it (and the entire bar in which it sits) would allow more folder content to be displayed. Search would need to be added to a menu, probably the Tools menu, to bring up the Advanced Search dialog.