In case you need to override manually
$ sudo rm /usr/share/indicators/messages/applications/evolution $ sudo bash -c "echo /usr/share/applications/thunderbird.desktop > /usr/share/indicators/messages/applications/thunderbird"
In case you need to override manually
$ sudo rm /usr/share/ indicators/ messages/ applications/ evolution applications/ thunderbird. desktop > /usr/share/ indicators/ messages/ applications/ thunderbird"
$ sudo bash -c "echo /usr/share/