Merged PR 12965: set encoding 'utf-8' on Message

**This is a workaround for encoding issue until Magento resolves bug**
magento/magento2#22065
magento/magento2#22103

**Change will effect Magento 2.2.8 and 2.3.+**
Because of ZF v2 usage in these versions setEncoding on message should fix encoding overall (setEncoding fixes encoding issue in subject) but because of ZF v2 bug have to fix encoding separately on body.
zendframework/zendframework#6841
zendframework/zendframework#5708
zendframework/zendframework#4917

**To test:**
- Test both email types text and html
- Test in Magento 2.3.*
- Test in Magento 2.2.8
- Test in Magento < 2.2.8
- Test using our Email Template mapped and our SMTP enabled
- Test using Magento template and our SMTP enabled
- Test using our SMTP disabled

Related work items: #86368

Model/Mail/SmtpTransportZend2.php

@@ -16,6 +16,11 @@ class SmtpTransportZend2
  */
  private $zendMailTransportSmtp2Factory;
 
+ /**
+ * Default encoding
+ */
+ const ENCODING = 'utf-8';
+
  /**
  * @param Transactional $transactionalEmailSettings
  * @param ZendMailTransportSmtp2Factory $zendMailTransportSmtp2Factory
@@ -29,13 +34,14 @@ public function __construct(
  }
 
  /**
- * @param \Magento\Framework\Mail\Message $message
+ * @param \Zend\Mail\Message $message
  * @param int $storeId
  */
  public function send($message, $storeId)
  {
  $smtpOptions = $this->transactionalEmailSettings->getSmtpOptions($storeId);
  $smtp = $this->zendMailTransportSmtp2Factory->create($smtpOptions);
+ $message->setEncoding(self::ENCODING);
  $smtp->send($message);
  }
 }

Plugin/MessagePlugin.php

@@ -7,6 +7,9 @@
 use Magento\Email\Model\TemplateFactory;
 use Magento\Framework\Mail\MessageInterface;
 use Magento\Framework\Registry;
+use Zend\Mime\Mime;
+use Zend\Mime\Part;
+use Dotdigitalgroup\Email\Model\Mail\SmtpTransportZend2;
 
 class MessagePlugin
 {
@@ -51,11 +54,11 @@ public function __construct(
 
  /**
  * @param MessageInterface $message
- * @param string $body
+ * @param mixed $body
  *
  * @return mixed
  */
- public function afterSetBody(MessageInterface $message, $body)
+ public function beforeSetBody(MessageInterface $message, $body)
  {
  $templateId = $this->isTemplate();
  if ($templateId && $this->shouldIntercept()) {
@@ -64,8 +67,37 @@ public function afterSetBody(MessageInterface $message, $body)
  $this->handleZendMailMessage($message);
  $this->setMessageFromAddressFromTemplate($message, $template);
  }
+ if (is_string($body) && ! $message instanceof \Zend_Mail) {
+ return [self::createMimeFromString($body)];
+ }
  }
- return $body;
+ return null;
+ }
+
+ /**
+ * @param $string
+ * @return bool
+ */
+ private function isHTML($string)
+ {
+ return $string != strip_tags($string);
+ }
+
+ /**
+ * Create HTML mime message from the string.
+ *
+ * @param string $body
+ * @return \Zend\Mime\Message
+ */
+ private function createMimeFromString($body)
+ {
+ $bodyPart = new Part($body);
+ $bodyPart->setEncoding(Mime::ENCODING_QUOTEDPRINTABLE);
+ $bodyPart->setCharset(SmtpTransportZend2::ENCODING);
+ ($this->isHTML($body)) ? $bodyPart->setType(Mime::TYPE_HTML) : $bodyPart->setType(Mime::TYPE_TEXT);
+ $mimeMessage = new \Zend\Mime\Message();
+ $mimeMessage->addPart($bodyPart);
+ return $mimeMessage;
  }
 
  /**