MC-33700: TransportBuilder unable to send emails of Content-Type "text/plain"

Author: Roman Lytvynenko

lib/internal/Magento/Framework/Mail/Template/TransportBuilder.php

@@ -12,9 +12,8 @@
 use Magento\Framework\App\TemplateTypesInterface;
 use Magento\Framework\Exception\LocalizedException;
 use Magento\Framework\Exception\MailException;
-use Magento\Framework\Mail\EmailMessageInterface;
-use Magento\Framework\Mail\EmailMessageInterfaceFactory;
 use Magento\Framework\Mail\AddressConverter;
+use Magento\Framework\Mail\EmailMessageInterfaceFactory;
 use Magento\Framework\Mail\Exception\InvalidArgumentException;
 use Magento\Framework\Mail\MessageInterface;
 use Magento\Framework\Mail\MessageInterfaceFactory;
@@ -28,7 +27,7 @@
 use Magento\Framework\Phrase;
 
 /**
- * TransportBuilder
+ * TransportBuilder for Mail Templates
  *
  * @api
  * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
@@ -380,11 +379,11 @@ protected function prepareMessage()
 
         switch ($template->getType()) {
             case TemplateTypesInterface::TYPE_TEXT:
-                $part['type'] = MimeInterface::TYPE_TEXT;
+                $partType = MimeInterface::TYPE_TEXT;
                 break;
 
             case TemplateTypesInterface::TYPE_HTML:
-                $part['type'] = MimeInterface::TYPE_HTML;
+                $partType = MimeInterface::TYPE_HTML;
                 break;
 
             default:
@@ -395,10 +394,10 @@ protected function prepareMessage()
 
         /** @var \Magento\Framework\Mail\MimePartInterface $mimePart */
         $mimePart = $this->mimePartInterfaceFactory->create(
-        	[
-        		'content' => $content,
-        		'type' => $part['type']
-        	]
+            [
+                'content' => $content,
+                'type' => $partType
+            ]
         );
         $this->messageData['encoding'] = $mimePart->getCharset();
         $this->messageData['body'] = $this->mimeMessageInterfaceFactory->create(