My Mail App hangs when I start it up right after SmapSieve launches. If I force quit SpamSieve before it gets a chance to launch the mail app opens just fine. I have tried deleting the file you suggested above and restarting. The Mail app hangs again.
Addition to above comment
It does not crash - it simply hangs with the spinning icon so I do not have a crash report to upload.
It would be helpful if you could open the Activity Monitor program and select Mail in the list. When it hangs, choose Sample Process from the View menu. Then save the resulting data to a file and send it to me.