Hi,
I'm gonna add my 2 cents for Mozilla 1.3a too. I've been using it since the first of the year. I should go get the new 1.4 but I haven't had time yet.
I love it! The spam filters don't work quite right, but right enough to make it worth using. In my case...(maybe it's because it's on Linux) the spam is marked with the junk icon, but it isn't moved out of my inbox to the junk box. But, since it's marked, I use the tool menu to select the run junk filters option and off it goes..enmass.
Otherwise...just as Dick says, even this "alpha" version of Mozilla works _very, very_ well. I would recommend anyone on any operating system give it a try.
see ya,