minor #21193 [Mailer] Fix Mailer #21190 : Update documentation about allowed_recipients behaviour (jordanaubert)

This PR was submitted for the 7.3 branch but it was merged into the 7.2 branch instead.

Discussion
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[Mailer] Fix Mailer #21190 : Update documentation about `allowed_recipients` behaviour

Fix #21190 Mailer issue

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b0d3f22 Fix Mailer #21190 : Update documentation about `allowed_recipients` behaviour

Author: javiereguiluz

mailer.rst

@@ -1926,9 +1926,8 @@ a specific address, instead of the *real* address:
             ;
         };
 
-Use the ``allowed_recipients`` option to specify exceptions to the behavior defined
-in the ``recipients`` option; allowing emails directed to these specific recipients
-to maintain their original destination:
+Use the ``allowed_recipients`` option to specify a "whitelist": this will allow emails directed to these specific recipients
+to maintain their original destination, as well as being sent to the destinations defined in ``recipients``:
 
 .. configuration-block::
 
@@ -1988,8 +1987,8 @@ to maintain their original destination:
         };
 
 With this configuration, all emails will be sent to ``youremail@example.com``,
-except for those sent to ``internal@example.com``, ``internal-monitoring@example.fr``,
-etc., which will receive emails as usual.
+and in addition, those sent to ``internal@example.com``, ``internal-monitoring@example.fr``,
+etc., will receive emails as usual.
 
 .. versionadded:: 7.1