$url    = parse_url($string);
                $host = $url['host'];
                $host = explode(".",$host);
                
                  // Normale Domain (www.google.de) oder (subdom.google.de)
                
                if(strlen($host[0]) > 0 AND strlen($host[2]) > 0) {
                    
                    if((preg_match('/^[a-zA-Z0-9\-\_]+$/',$host[1]))) {
                        
                        if(!function_exists('checkdnsrr')) {
                            
                            $ho = $host[1].".".$host[2];
                            
                            function checkdnsrr($ho, $type = '') {
                                if(!empty($ho)) {
                                    if($type == '') $type = "MX";
                                        @exec("nslookup -type=$type $ho", $output);
                                        while(list($k, $line) = each($output)) {
                                            if(eregi("^$ho", $line)) {
                                                return true;
                                            }
                                           }
                                           
                                           return false;
                                      }
                                   }
                            }
                        
                        if(checkdnsrr($host[1].".".$host[2].'.', 'MX') ) return true;
                           if(checkdnsrr($host[1].".".$host[2].'.', 'A') ) return true;
                           if(checkdnsrr($host[1].".".$host[2].'.', 'CNAME') ) return true;
                        
                    }else { return false; }    
                
                // Normale Domain ohne www (google.de) oder (google.de)
                    
                }elseif(strlen($host[0]) > 0 AND strlen($host[2]) == 0) {
                
                    if((preg_match('/^[a-zA-Z0-9\-\_]+$/',$host[0]))) {
                        
                        if(!function_exists('checkdnsrr')) {
                            
                            $ho = $host[0].".".$host[1];
                            
                            function checkdnsrr($ho, $type = '') {
                                if(!empty($ho)) {
                                    if($type == '') $type = "MX";
                                        @exec("nslookup -type=$type $ho", $output);
                                        while(list($k, $line) = each($output)) {
                                            if(eregi("^$ho", $line)) {
                                                return true;
                                            }
                                           }
                                           return false;
                                       }
                                   }
                            }
                        
                        if(checkdnsrr($host[0].".".$host[1].'.', 'MX') ) return true;
                           if(checkdnsrr($host[0].".".$host[1].'.', 'A') ) return true;
                           if(checkdnsrr($host[0].".".$host[1].'.', 'CNAME') ) return true;
                        
                    }else { return false; }
                    
                }else { return false; }
                
                   return false;