dyndns + port forwarding + cobalt raq + mailproblem

Hi all,

I have setup an internal network with the IP range starting at 157.*.*.*.
There are dozens of PCs on this network. As well as some qubes and some Cobalt RAQs. One of these RAQs is a Sun Cobalt RAQ4, which should work as a mailhost. Hostname is (e.g. mailhost.mydomain.com).

To access the internet, we have setup a Bintec router. Furthermore I setup a dynamic domain name at dyndns.org.

So what I want to do now is the following:

- Every time the router connects to the internet it should also connect to dyndns and tell "this is my new ip".
working

- Setup a port forwarding on the router. router:80 to mailhost:80
working

- Now whenever I call mysubdomain.dyndns.org it should display the main page of the raq4 mailhost. And I want to send and receive mails via that dyndns address.

But as soon as I enter the dyndns.org address the browser tries to access the hostname and not the ip.

It says: Trying to connect to mailhost.mydomain.com.
But it should only go to the IP which is defined in the forwarding.
Why does he automaticaly try to connect to the host name??

Trying the same with one of my qubes it's working without a problem! I can reach the standard website of the qube. It also doesn't try to access the hostname as it does with the RAQ4. It simply opens the IP.

The mailhost is in use so I cannot restore the machine.

Do you have any hints???
Why does he try to connect to "mailhost.mydomain.com" instead of the IP??!?

thanks a lot in advance and kind regards

Sven