There is a serious problem with Mail. It crashed a hundred times with me as well.
So, first I deleted Flip4Mac. -> same problem.
I deleted plist -> Mail Enhancer doesn't work anymore
A friend told me later she had the same.
MacFixit has a small report as well about it.
Apple, are you going to fix this please???
Anyone has Mail Enhancer working again? I can't get it to work, so now no more small red mailcounts in the Dock icon
Now I cannot send mail out, although I could yesterday after setting up again my server settings.
This 10.4.4 is bad for Mail.