Issue #3391810: Attachment integration for MimeMail module style does not work

src/Plugin/Mail/SendGridMail.php

@@ -517,9 +517,9 @@ class SendGridMail implements MailInterface, ContainerFactoryPluginInterface {
     if (isset($message['params']['attachments']) && !empty($message['params']['attachments'])) {
       foreach ($message['params']['attachments'] as $attachment) {
         $attach = new Attachment();
-        if (isset($attachment['uri'])) {
+        if (isset($attachment['filepath'])) {
           $attachment_path = \Drupal::service('file_system')
-            ->realpath($attachment['uri']);
+            ->realpath($attachment['filepath']);
           if (is_file($attachment_path)) {
             try {
               $struct = $this->getAttachmentStruct($attachment_path);