I have just had this problem and un ticked the device admin choice for mail. It deleted the account in email so I downloaded OWA and it doesn't take over the security of the whole system, it seems to be self contained for security.
Re: How to remove an account from the EMail app in Kitkat? "Remove Account" option has vanished.
Just a note about an exchange account being device administrator, on mine it also greyed out the lock screen options except for password and pin. It broke a tasker profile I was using so I deleted...