anchor.diff:      myorigin = ${cfg.origin}
     '')
     + optionalString (cfg.destination != null) (''
  -    mydestination = ${toString cfg.destination}
  +    mydestination = ${concatStringsSep ", " cfg.destination}
     '')
     + optionalString (cfg.relayDomains != null) (''
  -    relay_domains = ${toString cfg.relayDomains}
  +    relay_domains = ${concatStringsSep ", " cfg.relayDomains}
     '')
     + ''
       local_recipient_maps = 
  
positive.code:   +
    (if cfg.networks!=null then
      (''
        mynetworks = ${toString cfg.networks}
      '') 
    else if (cfg.networksStyle != "") then
      (''
  
negative.code:   idList = import ../system/ids.nix;
  
    optionalString = pkgs.lib.optionalString;
    concatStringsSep = pkgs.lib.concatStringsSep;
    mainCf = 
    ''
      queue_directory = /var/postfix/queue
  