title: Need not standard postfix configuration
body: <p>The task turned out to raise the relay postfix, which can send messages from mynetworks, to attempts to send messages through it to the domain from other hosts, it
  should issue 451. At the same time, NDR should be sent from it to the internal mail servers.
  Please suggest how to implement it.
  There were no problems with setting up opendkim, but there is not enough experience.</p>