Update mailer.rst

Add Tips for special characteres for user and pass

Author: cadjou

mailer.rst

@@ -65,6 +65,10 @@ over SMTP by configuring the DSN in your ``.env`` file (the ``user``,
             ]);
         };
 
+.. caution::
+
+    If your user or password has special characters such as @ or #, use encoding characters such as% 40 or% 23.
+
 .. caution::
 
     If you are migrating from Swiftmailer (and the Swiftmailer bundle), be