Get Server Fully-Qualified Domain Name.

function GetPublicHostname()
{
    $ipProperties = [System.Net.NetworkInformation.IPGlobalProperties]::GetIPGlobalProperties()

    if ($ipProperties.DomainName -eq "")
    {
        return $ipProperties.HostName
    }
    else
    {
        return "{0}.{1}" -f $ipProperties.HostName, $ipProperties.DomainName
    }
}