In this Blog we will discuss some scenarios when user can get this error message and solution to fix Outlook Mac Error Code 17997. However, sometimes you may get the error message “Unexpected data was encountered” while connecting Mac Outlook 2011 to Exchange Server and if you will check the error log you will see “mail could not be sent” with the error code -17997 or “Outlook Mac Error Code 17997” may appear on your screen when you try to send emails from MS Outlook for Mac 2011 Exchange Account. For offline accessing mail through Outlook on Mac you need to connect it with Exchange Server.