I switched from Eudora to T-bird several years ago and it was an excellent move. There are only a few deficiencies in T-bird, so it is not quite a 5 star, but a 4.5 for me. My biggest complaint about it is the occasional failure to update the preview pane when I select another email and I must select a different email, then try it again and it always works that way the second time I select it. All my Gmail labels appear as folders in T-Bird and it handles that well. I use it with Gmail, yahoo, GoDaddy, Outlook (Hotmail), and other servers.
I don't understand why everybody loves it so much. The default Windows 8.1 Mail app is much better. Here the layout isn't comfortable to use and it takes too much time to sync. On Linux I prefer Geary.