I am looking for a solution to a problem that I am having. I need to be able to render transactional emails for Magento 2.1.9 but they don’t need to be sent. I need to pass the email content to an internal API. I have googled and found nothing that can point me in the right direction to get the rendered email template.

I have tried to use the following to get the rendered email and I am not having any luck.

 $  transport = $  this->_transportBuilder                 ->setTemplateIdentifier($  templateId)                 ->setTemplateOptions(['area' => Area::AREA_FRONTEND, 'store' => $  storeid])                 ->setTemplateVars($  vars)                 ->setFrom($  identity)                 ->addTo($  cusomterData['email'], $  cusomterData['firstname']." ".$  cusomterData['lastname'])                 ->getTransport(); 

I var_dump transport and its null. I looked in the lib/internal/Magento/Framework/Mail/Template/TransportBuilder.php to see what it was doing and in the ->getTransport method I see that its doing the following:

 public function getTransport() {     $  this->prepareMessage();     $  mailTransport = $  this->mailTransportFactory->create(['message' => clone $  this->message]);     $  this->reset();      return $  mailTransport; } 

I need to be able to email content when ever the state of the order changes from the following pending, processing, completed.

I am using a custom observer that fires on sales_order_save_after. The observer works I can get the order data and status. I just at a loss for how to get the rendered html content for the email.

If someone can point me in the right direction it would be a great help to me.