Thunderbird has my Funambol plugin so I can sync with my Blackberry. Evolution handles signatures in a way that I agree with. Thunderbird looks nicer. Evolution doesn’t need to be told to fetch messages from all of my IMAP folders Thunderbird has superior message threading. Evolution is a Gnome app. Thunderbird can mark messages deleted, instead of moving them to some weird Trash folder. Thunderbird doesn’t have the ugliest default addressbook of all time.