!fixup bugfix thanks to @mclaeysb

pos_mail_receipt/static/src/js/screens.js

@@ -79,14 +79,14 @@ odoo.define("pos_mail_receipt.screens", function (require) {
                             'title': error.data.message,
                             'body':  error.data.debug
                         });
-                         this.$('.button.email').removeClass("highlight");
+                         self.$('.button.email').removeClass("highlight");
                     }
                     if(connection_problem){
                         self.gui.show_popup('error',{
                             'title': _t('The e-mail could not be sent'),
                             'body': _t('Check your internet connection and try again.'),
                         });
-                         this.$('.button.email').removeClass("highlight");
+                         self.$('.button.email').removeClass("highlight");
                     }
                 });
         },