set_action()
  An interscanner to return a status to set an action to return.
  
  You can user this scanner to set default policy returned by policy scanner,
  or you can set policy according to scanner reply.
  
  Usage: set_action(action, *scanners)
  
  Where: action can be an action defined in postfix's SMTPD_POLICY_README,
           for example: dunno, defer_if_permit, ok, reject, ...
  
  New in version 0.8.0.