anchor.diff:    virtualFile = pkgs.writeText "postfix-virtual" cfg.virtual;
     checkClientAccessFile = pkgs.writeText "postfix-check-client-access" cfg.dnsBlacklistOverrides;
     mainCfFile = pkgs.writeText "postfix-main.cf" mainCf;
  -  masterCfFile = pkgs.writeText "postfix-master.cf" masterCf;
  +  masterCfFile = pkgs.writeText "postfix-master.cf" masterCfContent;
     transportFile = pkgs.writeText "postfix-transport" cfg.transport;
  +  headerChecksFile = pkgs.writeText "postfix-header-checks" headerChecks;
   
   in
   
  
positive.code:         description = "contents of check_client_access for overriding dnsBlacklists";
        };
  
        extraMasterConf = mkOption {
          type = types.lines;
          default = "";
          example = "submission inet n - n - - smtpd";
          description = "Extra lines to append to the generated master.cf file.";
        };
  
        aliasFiles = mkOption {
  
negative.code:         ";
        };
  
        aliasMapType = mkOption {
          type = with types; enum [ "hash" "regexp" "pcre" ];
          default = "hash";
          example = "regexp";
          description = "The format the alias map should have. Use regexp if you want to use regular expressions.";
        };
  
        config = mkOption {
          type = with types; attrsOf (either bool (either str (listOf str)));
          default = defaultConf;
          description = ''
            The main.cf configuration file as key value set.
          '';
          example = {
            mail_owner = "postfix";
            smtp_use_tls = true;
          };
        };
  
        extraConfig = mkOption {
          type = types.lines;
          default = "";
  