Merge branch '5.2' into 5.x

* 5.2:
  Added link to https://symfony.com/doc/current/mailer.html#configuring-emails-globally

Author: javiereguiluz

reference/configuration/framework.rst

@@ -3227,6 +3227,10 @@ headers
 Headers to add to emails. The key (``name`` attribute in xml format) is the
 header name and value the header value.
 
+.. seealso::
+
+    For more information, see :ref:`Configuring Emails Globally <mailer-configure-email-globally>`
+
 web_link
 ~~~~~~~~