symfony
diff --git a/‎src/Symfony/Component/Mime/Header/Headers.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Mime/Header/Headers.php
+2-2Lines changed: 2 additions & 2 deletions b/‎src/Symfony/Component/Mime/Header/Headers.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Mime/Header/Headers.php
+2-2Lines changed: 2 additions & 2 deletions
@@ -34,8 +34,8 @@ final class Headers
         'cc' => MailboxListHeader::class,
         'bcc' => MailboxListHeader::class,
         'message-id' => IdentificationHeader::class,
-        'in-reply-to' => UnstructuredHeader::class,
-        'references' => UnstructuredHeader::class,
+        'in-reply-to' => UnstructuredHeader::class, // `In-Reply-To` and `References` are less strict than RFC 2822 (3.6.4) to allow users entering the original email's ...
+        'references' => UnstructuredHeader::class, // ... `Message-ID`, even if that is no valid `msg-id`
         'return-path' => PathHeader::class,
     ];