Our current config is, we have an on-prem website living in the IIS of the on-prem MS Exchange server. No problem for the firewall, just forward all the ports to the Excahgne server's IP. But, we're moving to Exchange 2016, so we need the namespace for outlook anywhere.
So, what I want to do is, split off the exchange server from the web site, and put them on separate boxes. The question is, can I setup host headers or something similar in the inbound rules of our Meraki firewall? So that traffic to www.domain.com goes to 192.168.0.10, meanwhile mail.domain.com goes to 192.168.0.20
Or should I just break down and get an external web site for public consumption?
You could make this much simpler by hosting the web site externally such as in Amazon AWS or Azure. It's quite cheap. Also if the web site gets compromised at least they are not on the inside of your network.
Low cost, low complexity and good security - a winning trifecta.