Issue #3453660 by bceyssens: Use altered Mail message object

src/Plugin/Mail/SendGridMail.php

@@ -601,7 +601,7 @@ class SendGridMail implements MailInterface, ContainerFactoryPluginInterface {
 
     // Lets try and send the message and catch the error.
     try {
-      $response = $client->send($sendgrid_message);
+      $response = $client->send($sendgrid_params['message']);
     }
     catch (SendgridException $e) {
       $this->logger->error('Sending emails to Sendgrid service failed with error code ' . Xss::filter($e->getCode()));