Added cautionbox for sender

TODO: Same for "recipients", line 3141

Author: ThomasLandauer

reference/configuration/framework.rst

@@ -3132,8 +3132,11 @@ sender
 
 **type**: ``string``
 
-Sender used by the ``Mailer``. Keep in mind that this setting override a
-sender set in the code.
+Sender used as ``MAIL FROM`` in the SMTP session.
+
+.. caution::
+
+    This setting overrides a sender set in the code.
 
 recipients
 """"""""""