If not, you will not be able to use the EWS feature, as Outlook try to connects for the port 443, more information in the next Bugs:
Important note: EWS only works if you have the Proxy role installed and properly configured. To configure Outlook 2016 with EWS for Zimbra Collaboration need the next: Microsoft will release Office 2016 soon, this new Office have interesting new features: This is certified documentation and is protected for editing by Zimbra Employees & Moderators only.
