What ports to forward for mac mail server

Would the terminal command be: rdr pass on en2 inet proto tcp from any to any port 9999 -> 198.168.2.3 port 80 I would like to type in the following and be redirected to the web server on the NAS -> 152.1.2.3:9999 The easy solution is to connect the NAS directly to the network but I cannot because of local policies. I just cannot access it from outside the local network. I can access the webserver locally from my computer by entering 192.168.2.3 and it directs me to the webserver page at 192.168.2.3/Photos. My NAS can see the internet and get updates. I have Internet Sharing turned on and share my Ethernet connection of my macOS computer (152.1.2.3 on Ethernet 2) to my NAS (192.168.2.3 on Ethernet 1) The NAS has all traffic that comes in over HTTP directed to the correct folder (Photos). Specifically I would like to access the HTTP web server on my NAS at 192.168.2.3/Photos. I would like to port forward from my macOS Sierra computer with IP address of 152.1.2.3 to my NAS which is 192.168.2.3.

What ports to forward for mac mail server