So far, my reaction is “Feh.” Say what you will about Apple’s i-Apps, but they look pretty. Which is pretty important when most of what you do is look at it. Firefox isn’t as pretty as Safari, but its advantages are obvious. (To me. By “obvious” I mean I won’t explain — at least, not hear and now. Write me off as a troll if you wish.) But Thunderbird isn’t obviously better than Mail.app (mbox-format storage notwithstanding) and it is fabulously uglier.
So now I’m thinking about going to Mutt, which I used for years (1997-2003) on Linux. And that was in the fetchmail era. I remember how much better its message-threading was even then than Mail.app’s is today. Nowadays, it would appear that mutt can do POP and IMAP all by itself, and there are a variety of SMTP-pretenders suitable for sending stuff off your machine to someplace with a a real SMTP server. Plus, I suppose, spam-filtering of some kind or another.
(Maybe instead of Mutt I should use Sylpheed. It’s supposed to be like Mutt but with a GUI like Thunderbird. (Note I didn’t say a GUI like Mail.app.)
(Mail is step 237 of the ongoing migration. When I get this step done, there will only be two steps left: getting sound working, and being able to read and write DVDs. Then I can dump the iBook. Then I can buy a larger hard drive, and begin backing up the eMac.)
UPDATE: Mail.app apparently speeds up a lot when you do this.