Evolution needs to be running for the indicator to work
Binary package hint: evolution-indicator
The only way to have the messaging menu working is having Evolution in the foreground. This is annoying if you are doing anything else, such as browsing the web. Although you can minimize the window, it still takes space from the panel, which makes the messaging menu a bit pointless.
Evolution should be able to run in daemon mode, so that you can be notified of new emails without having the window open.
This bug may already be reported, but I couldn't find it.