Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 4280)
+++ wp-includes/pluggable.php	(working copy)
@@ -337,7 +337,7 @@
 
 	if ('' == $user->user_email) return false; // If there's no email to send the comment to
 
-	$comment_author_domain = gethostbyaddr($comment->comment_author_IP);
+	$comment_author_domain = @gethostbyaddr($comment->comment_author_IP);
 
 	$blogname = get_option('blogname');
 
@@ -415,7 +415,7 @@
 	$comment = $wpdb->get_row("SELECT * FROM $wpdb->comments WHERE comment_ID='$comment_id' LIMIT 1");
 	$post = $wpdb->get_row("SELECT * FROM $wpdb->posts WHERE ID='$comment->comment_post_ID' LIMIT 1");
 
-	$comment_author_domain = gethostbyaddr($comment->comment_author_IP);
+	$comment_author_domain = @gethostbyaddr($comment->comment_author_IP);
 	$comments_waiting = $wpdb->get_var("SELECT count(comment_ID) FROM $wpdb->comments WHERE comment_approved = '0'");
 
 	$notify_message  = sprintf( __('A new comment on the post #%1$s "%2$s" is waiting for your approval'), $post->ID, $post->post_title ) . "\r\n";