Apple Mail on Yosemite not syncing with Exchange Strange issue that neither my email provider not Apple could help with! so I come to you and hope you can solve the problem they could not!

I added the Exchange account in question a week or so ago. It functioned fine until there was an issue with syncing. I chcked forums and ppl suggested using the 'Rebuild' option. I did with resluts I cannot explain.

Apple Mail now refuses to recognise the inbox. It brings in messages from 2015 and nothing newer. This is clearly bizarre. I have removed the account and re-added and no matter what - I seem to get the same result. 

As a workaorund I added the account as an IMAP but I'd really like to get my exchange account working properly. Does anyone have any suggestions?

My only theory is that there is some file - some cached set of settings that is ruining my efforts to add a new account.

Anyone have any ideas? I'd be most grateful!
There looks to be changes made on exchange accounts that seem to affect mac osx 10. Yosemite.  Those who has this have a older version of apple mail client installed and the solution is to upgrade your mac to the highest version of mac os your device will take and the version of apple mail installed will work again with exchange accounts