Mac mail does not work after 10.8.5 update After installing Mountain Lion 10.8.5 update, mail does not associate to an email account and will not quit (Quit is grayed out - must force quit).  However, the email account is set up in preferences.  Library/mail/V2/maildata/accounts.plist lists the account and the Mailboxes are still present under Library/mail/V2/Mailboxes.  However, if I log out as iMac user and log in as another user, Mail works OK for a different email account associated to that user.  Does 10.8.5 limit the number of accounts for emails?  In Console, I get a MailIAPlugin message: "Tried to get settings for nonexistent account".  Any idea on how to get Mail to work?
Grayed out Quit in Mail usually indicates that mail is busy doing something (like sync) and does not allow quitting.

Here are few steps you can do:

1- Run the Connection doctor

2- Enable the Activity window to see what is going on (get mail)

3- Delete that account and recreate it. (no worry, your email should be on the original server (ie gmail), but better check that before.

4- Wait for it to complete its duty. (like updating 10000 emails)