If you are running Parallels Plesk Panel behind a standalone firewall, you might encounter certain problems with resolution of domain names served by Parallels Plesk Panel: when you set up a new DNS domain in the control panel, its zone file includes a resource record that associates the domain name with the IP address your Parallels Plesk Panel server is on, i.e. an internal network address like 192.168.1.1. As the 192.168.x.x IP addresses are reserved by the Internet Assigned Numbers Authority (IANA) for use by private networks, this domain name will not be accessible to the Internet users. To work around this, you would have to associate this domain name with the IP address of the firewall machine in the domain's zone file (Domains > domain name > DNS Settings).
We recommend using the DNS zone template (Home > DNS Settings) to automate association of the newly added domain names with appropriate IP addresses.
Let's consider setting up a Parallels Plesk Panel server running on 192.168.1.1 in a private network protected by a firewall, which is running on 11.22.33.44: