Magento only sends order confirmation emails when manually prompted to - php

Question

A Magento website I'm maintaining stopped sending order confirmations and/or invoices all of a sudden.
Nothing has been changed in the email settings and they're all complying with common Magento guidelines. I've tried sending a test email through the following php script to make sure it's not caused by any server settings:
<?php
$to = "me#domain.com";
$subject = "Test email";
$message = "This is a test email.";
$from = "testing#anothertest.test";
$headers = "From:" . $from;
if (mail($to, $subject, $message, $headers)) {
echo("Your message has been sent successfully");
} else {
echo("Sorry, your message could not be sent");
}
?>
The test message got delivered flawlessly.
I installed the SMTP Pro Email plugin to see if changing settings there would manage a result; nothing. The plugin offers the ability to send a test email, which again gets delivered without flaw.
Even stranger, clicking the 'Send Email' button in the Magento backend for an order does deliver the email. Signing up for a newsletter does result in a subscription confirmation request email. Clearly, the website can send mails, it just somehow doesn't get triggered to do so for order order confirmations and invoices.
And yes, both
System > Configuration > Sales > Sales Emails > Order > Enabled
and
System > Configuration > Sales > Sales Emails > Invoice > Enabled
are set to Yes and include a BCC address.
Similarly,
System > Configuration > Advanced > System > Mail Sending Settings > Disable Email Communications
is set to No.
I'm running Magento CE 1.6.2 on this site, so it's not the common cron job problem version 1.9 seems to cause for a lot of folk.
I'm racking my brain here, does anybody have a clue?

Answer 1

Still haven't found what causes the problem, but added some code to succes.phtml to force the mail to be sent upon loading that page:
<?php
$order = new Mage_Sales_Model_Order();
$incrementId = Mage::getSingleton('checkout/session')->getLastRealOrderId();
$order->loadByIncrementId($incrementId);
try
{
$order->sendNewOrderEmail();
} catch (Exception $ex) { }
?>
It's not the most elegant solution, but at least the customers get their order confirmation through this workaround.

Answer 2

I am using version 1.8.1. I have been fighting with this same problem for 2 weeks now. The simple solution came by me "enabling" every option in System > Configuration > Advanced. All the new order confirmations get sent out immediately now to the person placing the order.
Background: After installing and configuring the new Magento Cart, I noticed that emails were only going through if I manually sent them through the admin screens. This told me that the server SMTP settings were correct, but I was wondering why a person placing an order would not receive the confirmation email...ever. After much searching and reading I thought that it had to do with one of the other functions of the Magento cart. So I went into the system confuration under the advanced tab (System > Configuration > Advanced) and found that I had disabled certain things like Sendtofrined, Newsletter, etc. Not wanting to waste time at the moment, I simply went through the entire list and enabled everything. Now I have the coupon function, add to wish list function and newsletter stuff that I do not want to see in the cart, but the emails are going through immediately and reliably. I will now attempt to find which function is related to the order confirmation email by process of elimination. But this did the trick for me and I hope it helps someone else out there, without having to add code to the php files.