title: Send an email notification when custom order status changes in WooCommerce
body: <p>I have created a custom order status in my WooCommerce called Back Order (<strong><code>wc-backorder</code></strong>):  </p>
  
  <pre><code>/**
       * Add custom status to order list
  */
      add_action( 'init', 'register_custom_post_status', 10 );
      function register_custom_post_status() {
          register_post_status( 'wc-backorder', array(
              'label'                     =&gt; _x( 'Back Order', 'Order status', 'woocommerce' ),
              'public'                    =&gt; true,
              'exclude_from_search'       =&gt; false,
              'show_in_admin_all_list'    =&gt; true,
              'show_in_admin_status_list' =&gt; true,
              'label_count'               =&gt; _n_noop( 'Back Order &lt;span class="count"&gt;(%s)&lt;/span&gt;', 'Back Order &lt;span class="count"&gt;(%s)&lt;/span&gt;', 'woocommerce' )
          ) );
  
  }
  
  /**
   * Add custom status to order page drop down
   */
  add_filter( 'wc_order_statuses', 'custom_wc_order_statuses' );
  function custom_wc_order_statuses( $order_statuses ) {
      $order_statuses['wc-backorder'] = _x( 'Back Order', 'Order status', 'woocommerce' );
      return $order_statuses;
  }
  </code></pre>
  
  <p>Now I want to receive an email whenever an order is received that has been given the status quote. I've created a plugin based on this helpful article: <a href="http://www.skyverge.com/blog/how-to-add-a-custom-woocommerce-email/" rel="nofollow noreferrer">How to Add a Custom WooCommerce Email</a></p>
  
  <p><a href="https://github.com/sarun007/custom-email-plugin/tree/master" rel="nofollow noreferrer"><strong>This link</strong></a> is containing my plugin source code and the functions.php code.</p>
  
  <p>I added hook in <strong>function.php</strong>:</p>
  
  <pre><code>add_action( 'woocommerce_order_status_wc-order-confirmed', array( WC(), 'send_transactional_email' ), 10, 10 );
  
  function so_27112461_woocommerce_email_actions( $actions ){
      $actions[] = 'woocommerce_order_status_wc-order-confirmed';
      return $actions;
  }
  add_filter( 'woocommerce_email_actions', 'so_27112461_woocommerce_email_actions' );
  </code></pre>
  
  <p>Nothing happens when an order changed into the 'Back Order' status.</p>
  
  <p>Any ideas? </p>
  
  <p>I've tried loads of different hooks but I can't seem to get the trigger function to run.</p>
  
  <blockquote>
    <p>I am on latest versions of WordPress and WooCommerce (3.0+)</p>
  </blockquote>
  
  <p>Thanks</p>