DGFV338 Port Forwarding Problem

I'm trying to setup my DGFV to run a webserver from home, but seem to have hit a problem with the port forwarding.

Webserver is sat on a Mac OSX Lion Server, at internal IP 10.0.0.253.

So far I have set up a Firewall rule to send port 80 to 10.0.0.253.

In the configuration DNS Nameservers are set to 10.0.0.253 as primary and the secondary is the primary one prior to my entering the internal server. Internet functionality is working fine.

The Mac OSX Server rund its own DNS Server for the LAN.

DYNDNS is operating for external dns to resolve a FQDN to the dynamic IP.

The DGFV can be administered remotely on port 8081, and using www.mydomain.com:8081 I can see the router and login to it, which shows that DYNDNS is working effectively.

Internally I can type www.server1.mydomain.com and see the webserver welcome page (No site is setup as yet). Similarly if I type the internal IP (10.0.0.253) I get the welcome screen

But if I type either www.mydomain.com or www.server1.mydomain.com I get an error message when accessing from outside the LAN. If I type the ISP dynamically provided IP address, I get the same error.

Any suggestions of where my error is, since I suspect it is to do with the port forwarding setup.?????