A new problem I haven't experienced before is I can't add a Google Apps mail account in 10.9 If you add the account under System Preferences > Internet Accounts (choosing Google) it will add the contacts and calendar but the mail checkbox won't go. You get a popup error "Mail couldn't discover settings for account..." If you go to Mail > Preferences > Accounts and add it there, you get an error message about not being able to verify u/n and pwd. If I use Airmail, the account sets up on the first try. The only way I can get it to work in Mail is to duplicate the auto populated settings from Airmail. Mail > Preferences > Accounts and add it as "Add other email account". If you select Exchange that doesn't work either. Two other points, (1) this is for a Google Apps Gmail account not regular Gmail. My regular Gmail account sets up fine and (2) This did not happen in 10.8. It's new in 10.9. I also tried the Mail patch. No help.