I disagree strongly with Hangnail's contention that "Proper IMAP clients don't load all mail locally." That may work if one has a fast IMAP server (like he says he does) and without much mail stored on it. But it doesn't work if one has a slow IMAP server and has a lot of mail (1.25 GB in my case) stored on it.

Two or three years ago, I tried using Mulberry full-time for about 4-5 months, but gave up in frustration: Mulberry was making me wait 15-20 seconds to switch from one mailbox to another, and several minutes every time I did a search. If they ever modify Mulberry to cache mail locally, then I'll try it again, but not until then.