The order confirmation email is not sent

[ShapesGraphicStudio]

Hello,

I had an issue with 1.0.6 (#6), fixed in 1.0.7, but it seems to be back since 1.0.8 (with Magento 2.2.6).

My confirmation mails are not sent after payment.

After payment, status is OK at Processing.
In the orders notes I can see:
"You notified customer about invoice #XXXXXXX"

But Order & Account Information says "The order confirmation email is not sent".

We have customers feedback telling they did not get the messages.

Any idea on what could be wrong please ?

[ShapesGraphicStudio]

Well, looking a little further, "You notified customer about invoice #%1." seems to happen when email is sent:

if ($invoice && !$invoice->getEmailSent()) {
    ...
    $order->addStatusHistoryComment(__('You notified customer about invoice #%1.', $invoice->getIncrementId()))
                ->setIsCustomerNotified(true)
                ->save();
    ...
}

So the payment gateway seems to do the job..?

Why do I have "The order confirmation email is not sent" on the top of the order page in admin?

Configuration is OK, and server OK too.
As admin I receive the confirmation mails as my address is in "Send Invoice Email Copy To" field in the configuration.

Maybe I should just look at an SMTP service to upper my sending/receiving rates..?

Could you please confirm everything works OK in the gateway?
Can you confirm checkAndSend($order) returns true in file 'Magento\Sales\Model\Order\Email\Sender\OrderSender.php' using your gateway?

[ShapesGraphicStudio]

Hello @jcpaybox et @bm-services,
Could you please give me some information about the questions above ?