I managed to isolate one specific message and discovered that this message CAN BE RENDERED in Mail! So there's no system level problem! It's PowerMail! Also, there's NO SPAMSIEVE involved! It's the rendering.
I also tried importing this message into a new fresh otherwise empty database under a new user. Same crash! Next step is to check if this is true also on other Mac OS X machines. Stay tuned. Any volunteers for testing this specific message on their machines? In a new database of course, carefully evaluating the results.
