MAC with client certificate for Exchange

Certificates

Install root CA as written here

Double-click on it. It’ll launch the Keychain Access application and show you the following dialog box. Click on OK

install client certificate as written here

https://www.digicert.com/managing-client-certificates.htm#mac_importing_cert

You can validate in Keychain that the certificates are there 

The certificate as well as its root CA has to be trusted. After this change, restart the MAC

Outlook

Configure it to use client certificate