I had a very bad experience with Thunderbird and perhaps I just was just unlucky or inept, but I installed it on a new machine with W7, because Outlook Express, which I liked and was used to, is not compatible with W7 and I hated WLivemail..
Thunderbird deleted all the emails which I'd put into folders. Fortunately they were still on the server so I laboriously downloaded and sorted them again only to have the same happed. So I de-installed T/bird, re-installed it, set it all up, and it happened a third time. I am now frightened to use T/bird and still on Livemail and still hate it!