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