I have been trying to get back into mozilla recently. I got a tree built, it is very interesting to say the least to build mozilla on windows using cygwin. Now if we could only build with gcc on windows instead of vcc, but i suppose there are good reasons not to do that.
There is some very interesting work going on with mozilla and the browser. Maybe the mail client will receive something similar, though I must say the mail client is very nice and 1.0 promises to be an excellent release.