I don't like Thunderbird, so I installed Evolution. After starting the application I configured my email-account and everything seems to work without a problem.
Except for one really annoying thing: I can't maximize the window.
The maximize-button is missing. I also tried it via the window-menu, but even there the maximize-option is faded out. I also can't resize the window (it is possible to make it larger, but not smaller). But as I am a netbook-user I need to either maximize or at least resize the window to fit the screen.
I just installed Gnome-Shell and Evolution starts maximized. So I'd say, that this is a problem with Unity.
So to be honest, I don't know what I should, or could do.