code: def expand_variables(self, message):
          
          p = copy.deepcopy(self.data)
          if 'to_from' in self.data:
              to_from = self.data['to_from'].copy()
              to_from['url'] = to_from['url'].format(**message)
              if 'expr' in to_from:
                  to_from['expr'] = to_from['expr'].format(**message)
              p.setdefault('to', []).extend(ValuesFrom(to_from, self.manager).get_values())
          if 'cc_from' in self.data:
              cc_from = self.data['cc_from'].copy()
              cc_from['url'] = cc_from['url'].format(**message)
              if 'expr' in cc_from:
                  cc_from['expr'] = cc_from['expr'].format(**message)
              p.setdefault('cc', []).extend(ValuesFrom(cc_from, self.manager).get_values())
          return p
docs: expand any variables in the action to_from/cc_from fields.