Evolution's window has a gray bar at the bottom of its window, the status bar. It does two things: display a button on the left to switch from working online/offline and display messages temporarily, such as when it is downloading e-mails from the server.

I think the status bar is a waste of vertical space (which is precious now that widescreen monitors are so common) and it is better to remove it. I know the status bar can be hidden by choosing "View" → "Layout" → "Status Bar", but I argue it should be hidden by default and preferably removed entirely.

I don't know what others think, but I can't imagine any use case for online/offline button. I never use it and haven't noticed a similar button in other e-mail clients either. I think it could be removed, but if it needs to stay maybe it would be better to put it in the toolbar instead?

Regarding the notifications given by status bar, take a look at how most web browsers approach this. Many web browsers (Firefox for example) used to have a status bar, but no longer have one (Firefox currently doesn't even have an option to show it anymore).

In web browsers the status bar used to show the URL of a link if you hovered over one with the cursor. Even though the status bar is gone, it now shows the URL in a gray box in the lower left of the window if you hover over a link. The box is temporary and disappears as soon as you move the cursor. I think Evolution should copy this behavior: remove the status bar altogether and switch to temporary notifications.

Simply hiding the status bar is not a good idea as that will mean I lose the opportunity to see the notifications. That's why I think a small redesign is better.