NAT Reflection

I have a small home network that and I am running Astaro Security Gateway V8 home edition (no appliance).

How do I make NAT Reflection work?

For instance say my machines are all on mydomain.org
machine "server1" is running a web server that is port forwarded through the Astaro.

If workstation Y on my network browses to http://server1 the page will load. If workstation Y browses to http://mydomain.org from inside the network, the request times out. If workstation Z outside my network browses to http://mydomain.org it works fine, so the NAT settings are correct for that.

How can I get NAT reflection working? I tried creating a DNAT rule as follows

Traffic Souce: Internal Network
Traffic Service: HTTP
Traffic Destination: mydomain.org (and a different one with External WAN Address, neither worked)
NAT Mode: DNAT
Destination: server1
Destination Server: HTTP

but the HTTP requests aren't getting reflected back to server1. This hasn't been an issue with pfsense, smoothwall, dd-wrt or other routers so I'm hoping I'm just missing a setting.

Thank you for your help,
Matt