Too much space being taken up on the interface:
The top of mailbox. The interface. (doesn't matter, which browser used)
At the top of the mail interface, where you have the icon that says "yahoo!mail", and it has the yahoo search bar, and place for the account name, and the "Home" icon, this row is taking up entirely too much space.
The problem is magnified on a laptop, where there is limited space.
If you could reduce the space taken up by half, that would be great. It looks like there is plenty of elements that could be reduced in size.

You have the banner for "coming soon", which takes up space.
You also have some space, which is just blank (it shows some of the theme).
The row that has the yahoo!mail and search bar is too large, vertically. It would be better if you shrink the size to match the size of the home icon (house), that would reduce the space taken to allow more mail to be shown in the window.