Can not access web domain from local computers

I have a WEBserver IIS7 in my local network. When I go to "www.mydomain.com" from a computer inside same LAN I cant access it. If I put in the local IP it works. "www.mydomain.com" do also works from a different network. I guess there is some router isue. I use PFsense router.

pfSense calls it NAT reflection. That link is a page on pfSense's web site showing how to turn that on. That page also shows how to turn on an alternate solution, Split DNS, that lets you override DNS entries, so internally www.mydomain.com goes directly to the machine hosting the site without going out to the internet. It's basically like editing /etc/hosts except it applies to all machines in your network. While that will make reaching your server faster and will work even if your internet connection is down, it means you won't be hitting your site in the same way as other external users, which you may not want to do for testing purposes. Either method should work though, it just depends on your use cases which you want to use.