minor #15240 [Mailer] Added cautionbox for sender (ThomasLandauer)

This PR was submitted for the 5.2 branch but it was merged into the 5.3 branch instead.

Discussion
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[Mailer] Added cautionbox for sender

TODO: Same for "recipients", line 3141

Commits
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adba2b8 Added cautionbox for sender

Author: javiereguiluz

reference/configuration/framework.rst

@@ -3373,8 +3373,11 @@ 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
 """"""""""