Exchange 2016 ActiveSync in Edge Server

Exchange Edge Transport servers only do mail flow (SMTP) and anti-spam protection.

If you want publish ActiveSync to the internet, then there are only two options for you:

• forward HTTP and HTTPS ports on the firewall directly to Exchange servers (which you don't want to do)
• install a reverse web proxy in your DMZ. Microsoft IIS + ARR or Microsoft WAP support HTTP(S) proxying and are free with Server OS. But any reverse web proxy will do.

I don't believe there is an official Microsoft documentation on how to configure IIS ARR or WAP to publish Exchange in DMZ. But you can easily find several unofficial how-to-s out there