$email = Mage::getModel('core/email_template');
$customerEmail = $_order→getCustomerEmail();
$storeId = Mage::app()->getStore()->getStoreId();
$emailTemplateVariables = [
'order' => $_order
];
try {
$email→sendTransactional(
'payment_reminder_template',
$sender,
$customerEmail,
$sender,
$emailTemplateVariables
);
} catch (Exception $error) {
Mage::getSingleton('core/session')->addError($error→getMessage());
}