If you are using Microsoft Exchange as your storage destination, you must configure Exchange Web Services (EWS) to ignore client certificates. EWS provides the functionality to enable client applications to communicate with the Exchange server. EWS provides access to almost all data that is available through Microsoft Office Outlook.
By ignoring client certificates, any system can establish a connection to the EWS component and after authentication access the EWS component. For more information, see the Microsoft Exchange Server website.