<?php
/*
 * Plugin Name: Disable Auto Update Mails
 * Plugin URI: http://al.id.au/svn/tools/web/wordpress/mu-plugins/selective-auto-update-mail.php
 * Version: 1.0
 * Author: Alastair Irvine <alastair@plug.org.au>
 * AuthorURI: http://al.id.au/
 * */

add_filter( 'auto_core_update_send_email', 'check_update_success', 10, 2 );

/**
 * Only returns true if the update was NOT successful, i.e. causes e-mails to be sent when @p $type 
 * is 'fail', 'critical'.
 */
function check_update_success($send, $type)
{
  return $type != 'success';
}