Erase Mail settings and import mailboxes
I don't know what else to do to solve the problem? I've tried deleting all cache and repairing permissions, etc. It must be something with the mail preferences or settings!?!?!?
Thanks in advance
Close Mail, move the file com.apple.Mail.plist from the folder <home>/Library/Preferences to the Desktop and re-start Mail. It will start up as if it has never been configured before and ask you to create your primary email account. If you have more than one email account you can add them via Mail Preferences after Mail loads.
Your old messages (the ones under "ON MY MAC") are stored in the folder <home>/Library/Mail/Mailboxes and should remain unaffected but if you are a bit nervous about losing any of those messages then drag the folder <home>/Library/Mail to your Desktop so that you can import the messages after you have set up your accounts as per above.