diff --git a/mailer.rst b/mailer.rst
index ec13d48e4ba..8aa3f82acb7 100644
--- a/mailer.rst
+++ b/mailer.rst
@@ -944,8 +944,9 @@ This can be configured by replacing the ``dsn`` configuration entry with a
             ],
         ]);
 
-By default the first transport is used. The other transports can be used by
-adding a text header ``X-Transport`` to an email::
+By default the first transport is used. The other transports can be selected by
+adding an ``X-Transport`` header (which Mailer will remove automatically from
+the final email)::
 
     // Send using first "main" transport ...
     $mailer->send($email);