diff --git a/src/Entity/MessageDocument.php b/src/Entity/MessageDocument.php
index efa1b040..37808e86 100644
--- a/src/Entity/MessageDocument.php
+++ b/src/Entity/MessageDocument.php
@@ -55,6 +55,9 @@ class MessageDocument implements EntityInterface, MonitorableEntityInterface, Ui
             'png',
             'webp',
         ],
+        'message' => [
+            'rfc822',
+        ],
         'text' => ['*'],
     ];