In Mac OS X 10.4 Tiger, if Mail (or any other application, but Mail is our focus here) unexpectedly quits twice in a row, you will be given the opportunity to open the application with the default ("safe") settings by clicking a Try Again button in a dialog that appears when you open Mail a third time.
In the unlikely event that Mail unexpectedly quits twice in a row, clicking the Try Again button should successfully open Mail. You will then be guided through setting up your Mail account (or accounts) again. Your previous Mail messages will appear after you complete the account set-up (assuming that you've set up the same account that you were using before).
Important: If you enter different account information than before, Mail will not show messages for the account you were using prior to the two unexpected quits. But it doesn't delete those missing messages either—they'll be available once you set up that account again in Mail preferences.
For example, let's say that you use a POP server-based Mail account named MyMail for the address myfakeaddress@fakeplace.com, and have many messages in your Inbox. If Mail unexpectedly quits twice in a row and you click Try Again when opening Mail a third time, Mail will open and ask you to fill in your account information. If you fill in the same "MyMail" account information, you'll have access to your "MyMail" messages. If you fill in different information, such as an IMAP server or address of myfunaddress@funfakeplace.com, you won't see your original "myfakeaddress@fakeplace.com" messages until you set up the account the same way it was before.
Alternatively, if messages are missing after using the Try Again button, you could import the mailboxes from ~/Library/Mail.
Related Terms: forgot, forgets, crash, crashing, crashed, email