when sendOrderUpdateEmail function work?

Question

I have sendOrderUpdateEmail in my module but this function, some times work and send email and some times,NOT.

I think this work if for example my prev. status was "NEW"

In which status, this function work and send update email to customers?

If I want to send update email for all status, how can I use this method in my module?

I used same as below in my module

$comment = $helper->__("Order status changed to: %s", $newState);
$order->setData('state', $status);
$order->setStatus($order->getConfig()->getStateDefaultStatus($status));
$history = $order->addStatusHistoryComment($comment, false);
$history->setIsCustomerNotified(true);
$order->sendOrderUpdateEmail(true, $comment);
$order->save();

Answer 1

The most probably it will not help, but check following.

Here is your function:

public function sendOrderUpdateEmail($notifyCustomer = true, $comment = '')
{
    $this->queueOrderUpdateEmail($notifyCustomer, $comment, true);
    return $this;
}

This function calls queueOrderUpdateEmail

/**
 * Queue email with order update information
 *
 * @param boolean $notifyCustomer
 * @param string $comment
 * @param bool $forceMode if true then email will be sent regardless of the fact that it was already sent previously
 *
 * @return Mage_Sales_Model_Order
 */
public function queueOrderUpdateEmail($notifyCustomer = true, $comment = '', $forceMode = false)

In default magento this function calls with forceMode equals true. Maybe you have forceMode = false and according to description the letter will not send if it was sent by somehow.

Also you can try to put some Mage::log inside queueOrderUpdateEmail and determine why is it happening. If you need any help regarding this - just ask.