I have eight (I think) fixed IP addresses (a block?). I only use one.
I have one Fritz!Box router where I port forward mail 'n' stuff to a local server.
But say, for legitimate but complex reasons, I need to run another mail server on another server on my LAN. How - using the tools I have - can I route mail for @thisdomain to ThisServer using port forwarding while also sending mail for @thatserver to ThatServer.
In Fritz!Box I can add a "Public IPv4 Subnet", it says
"If your internet service provider supplies you with a public IPv4 subnet, you can enter it here."
So, if I have the DNS setup for thisserver.tld to point to ThisServer I can also do the same for ThatServer.
But the Fritz!Box instructions appear to say ThatServer won't be on my LAN anymore. "Network devices that are assigned a public IP address no longer obtain their IP settings from the FRITZ!Box. Therefore, they cannot access other devices in the FRITZ!Box home network or the FRITZ!Box user interface." It's not the same as the post forwarding I have set up already which goes to a 'server' I can access locally on my LAN.
Am I Very Confused? Or have I got this Spot On? Or maybe there's a Better Way?