add forward-confirmed reverse DNS

inc/config.php

@@ -66,7 +66,10 @@
 	// Use `host` via shell_exec() to lookup hostnames, avoiding query timeouts. May not work on your system.
 	// Requires safe_mode to be disabled.
 	$config['dns_system'] = false;
-	
+
+	// Check validity of the reverse DNS of IP addresses. Highly recommended.
+	$config['fcrdns'] = true;
+
 	// When executing most command-line tools (such as `convert` for ImageMagick image processing), add this
 	// to the environment path (seperated by :).
 	$config['shell_path'] = '/usr/local/bin';