I would like to use Evolution as the default mail client. Thus, I'd like to have Evolution integrated with the desktop instead of Thunderbird (especially concerning the mail symbol on the desktop bar). Has anyone experience 'reverting' to Evolution?

I did change the Mail client setting in the Default Applications section in System Info dialog from 'Thunderbird' to 'Evolution'. This has the effect that the mail application started from Unity Launcher is indeed Evolution, yet, this setting does not replace Thunderbird with Evolution in the desktop bar. And, it does not enable desktop notifications for Evolution, as a consequence.