I guess since I use Firefox as my browser, it might also follow that I'd use Thunderbird as my mail client. Yeah, that's me. I was using Netscape since way back when. I used the Mozilla suite when it more or less replaced Netscape. Sometime after Firefox and Thunderbird got underway I began using them as well.
In the beginning, I was a little leery of making the change. But it wasn't too hard to switch since the profiles transferred over with no pain. I haven't looked back.
Well, that might be a slight over statement. But it was very slight. I had some issues in the very early days, but they were so small I can't remember what they were. Really.
So why do I use Thunderbird? Because it's simple. Outlook Express (OE) can be simple--sort of--but it's also got a bit too much baggage. To have a simple OE install, it requires too much work after the initial install. I don't have to worry about that with Thunderbird. It starts simple and only gets complex if I make it that way! The only thing that OE has that Thunderbird does not is HotMail integration. But that's a small price to pay.
You can get Thunderbird here.
There's a lot more that I really should say. I'll re-visit this later.