It would be very helpful if you created a possibility to distinguish the accounts in the folder pane by using different colors.
The layout (composition) of the emClient is not quite clear and user-friendly because of no possibility of personalization, all the details in the folder pane are not enough readable, the seem to blur and fuse into one account.
There also should be an option to use only icons in the menu.
Generally the layout is too flat and monotonous. The tabs should be more colorful and 3D or at least 2D when pointed out by a user.