After installing the latest security update on Mac OS X 10.5.6, Mail began to crash on startup. It printed out the message saying the problem may be because of the GrowlMail plugin. Disabling the Growl and removing the GrowlMail plug-in didn’t help. I’d to remove the GrowlMail.mailbundle from both the ~/Library/Mail/Bundles and /Library/Mail/Bundles. Now the Mail is running fine. I stopped using GrowlMail sometime back, when it started “growling” for all the old messages, it was annoying and becoming similar to Windows notifications.
Update: The issue has been posted on GrowlMail’s forum