Every now and then some fault in Apple's Mail application results in it not launching correctly, and sometimes resulting in the application unexpectedly quitting.
Per Apple Discussions poster Wesley108
"Everytime I click on Mac mail, the application 'quits unexpectedly' ... I've reported the problem over and over. Once in a while it gives me the option to 'reset the settings and relaunch' and I try that but nothing. I've also rebooted. Also, have updated everything."
Mail launching problems can result from several problems, including faulty settings, or problematic messages or message contents. If a message loads at start which has corrupted images or other content, Mail will attempt to load the content and each time will run into problems. Likewise, corrupt preference files can also cause similar problems. In addition, newer versions of Mail have included support for extended messaging features such as ToDo items and Notes, and if there are errors in how these items are stored or accessed, Mail can be adversely affected.
FixesRemove ToDo itemsUsers might check the console application for the Mail crash log (listed under "CrashReporter" in the Console application) if the problem occurs. If the crash log lists something such as "trying to set a non-ToDo MailboxUid for a ToDo", then users might try removing accumulated ToDo items. These items are available both in Mail as well as iCal, so users can remove them by opening iCal and deleting them from that application. It's recommended to list all ToDo items and then cut them using the "Edit" menu instead of outright deleting them. Then quit iCal and attempt to open Mail again. If this does not fix the problem, users can then open iCal and paste the previously cut ToDos back into the application.
Troubleshoot messages loaded at startup If a message contains corrupt content (pictures or attachments) that are causing problems, users can prevent the messages from loading at application launch by holding the shift key directly after launching Mail. From here users can troubleshoot mail messages to see if any cause the program to hang or crash, and remove any problematic messages causing such behavior.
Remove preference files and troubleshoot accounts If the first two fixes do not address the problem, users can try removing the Mail application preferences, called com.apple.Mail.plist and located in the ~/Library/Preferences/ folder. Doing this will require mail account information to be reentered, but all previous messages and mailbox setups will remain and be visible again after account information has been supplied. In addition, Mail setup can be compared against that for a fresh account by creating a new user account and logging into that one. Then users can set up Mail and see if the problem persists. If it does not, then users know the problem has to do with their account and can troubleshoot the problem, targeting items in the ~/Library/Mail/ folder, or removing the contents of the ~/Library/Caches/Mail/ folder.Resources