Merge branch '5.4' into 6.2

* 5.4:
  [Mailer] add more info for debugging

Author: javiereguiluz

mailer.rst

@@ -641,6 +641,12 @@ provides access to the original message (``getOriginalMessage()``) and to some
 debug information (``getDebug()``) such as the HTTP calls done by the HTTP
 transports, which is useful to debug errors.
 
+.. note::
+
+    If your code used :class:`Symfony\\Component\\Mailer\\MailerInterface`, you
+    need to replace it by :class:`Symfony\\Component\\Mailer\\Transport\\TransportInterface`
+    to have the ``SentMessage`` object returned.
+
 .. note::
 
     Some mailer providers change the ``Message-Id`` when sending the email. The