Source link: https://social.msdn.microsoft.com/Forums/office/en-US/b14fe8bb-656e-468e-9346-881a7a13d548/need-to-stop-external-owa-on-exchange-2016-on-premises-environment?forum=exchangesvrdevelopment
We have exchange 2016 on Premises with 4 hosts with all the services on each server.
Internally, OWA and outlook can be operational. But from External network we need to stop publishing OWA.
Currently on external; OWA and autodiscover is published with port 443 and 80