Since upgrading to Yosemite my Mac mail inbox has been playing up. All the emails are there and show for a minute or two then the view changes and the inbox appears empty, selecting a different inbox (iCloud account, hotmail, Gmail) and going back to the Exchange inbox will make the message visible again. I have tried rebuilding, deleting the account and adding it again but all to no avail. New messages are coming in and all the mail is there it is just that they do not show (or more precise only show for a short period). This is the case both on my mid 2012 MBP and my mid 2013 MBA both running Yosemite version 10.10.