As if I didn’t have a crappy morning already, my Mac OS X Mail had to start bugging during my morning routines by the computer. After countless crash-reports and relaunches I even rebooted, but without success.
I found some hints on Google, including one on disabling Growl Mail. This seemed to be the most realistic solution, but didn’t work. I also tried many other suggested workarounds like deleting ToDos in iCal, clearing some caches, hitting some keys when Mail starts and so on. Nothing helped. After even more relaunching and sending bug reports to Apple, and another five minutes of Googling, I discovered a thread that had solved the problem by deleting the GrowlMail.mailbundle directory from HD/Library/Mail/Bundles.
Luckily, that worked for me as well. So now I can finally start my day and look forward to whatever else Murphy has got in store for me.