{ ... }: {
  # Postfix relay configuration, see: https://www.postfix.org/STANDARD_CONFIGURATION_README.html#backup
  services.postfix = {
    enable = true;
    hostname = "mail-2.grzb.de";
    relayDomains = [
      "grzb.de"
      "nekover.se"
    ];
    extraConfig = ''
      message_size_limit = 20971520
      smtpd_relay_restrictions = permit_mynetworks reject_unauth_destination
      proxy_interfaces = 217.160.117.160
      relay_recipient_maps =
    '';
  };
}