anchor.diff:    virtualFile = pkgs.writeText "postfix-virtual" cfg.virtual;
     mainCfFile = pkgs.writeText "postfix-main.cf" mainCf;
     masterCfFile = pkgs.writeText "postfix-master.cf" masterCf;
  +  transportFile = pkgs.writeText "postfix-transport" cfg.transport;
   
   in
   
  
positive.code:     ''
      + optionalString (cfg.virtual != "") ''
        virtual_alias_maps = hash:/etc/postfix/virtual
      ''
      + cfg.extraConfig;
  
  
negative.code:         default = "";
          description = "
            Entries for the virtual alias map, cf. man-page virtual(8).
          ";
        };
  
        transport = mkOption {
          default = "";
          description = "
            Entries for the transport map, cf. man-page transport(8).
          ";
        };
  
  