Index: modules/contrib/swiftmailer/src/Plugin/Mail/SwiftMailer.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- modules/contrib/swiftmailer/src/Plugin/Mail/SwiftMailer.php	(revision bff7b8e518c3a4ad9893a9baa1172b08df742428)
+++ modules/contrib/swiftmailer/src/Plugin/Mail/SwiftMailer.php	(revision )
@@ -590,7 +590,7 @@
     $line_endings = Settings::get('mail_line_endings', PHP_EOL);
     $message['body'] = Markup::create(implode($line_endings, array_map(function ($body) {
       // If $item is not marked safe then it will be escaped.
-      return $body instanceof MarkupInterface ? $body : Html::escape($body);
+      return $body instanceof MarkupInterface ? $body : preg_match("/<[^<]+>/",$body,$m) != 0 ? Html::escape($body) : $body;
     }, $message['body'])));
     return $message;
   }