anchor.diff:      (mkIf haveVirtual {
         services.postfix.mapFiles."virtual" = virtualFile;
       })
  +    (mkIf cfg.enableHeaderChecks {
  +      services.postfix.mapFiles."header_checks" = headerChecksFile;
  +    })
       (mkIf (cfg.dnsBlacklists != []) {
         services.postfix.mapFiles."client_access" = checkClientAccessFile;
       })
  +    (mkIf (cfg.extraConfig != "") {
  +      warnings = [ "The services.postfix.extraConfig option was deprecated. Please use services.postfix.config instead." ];
  +    })
     ]);
  -
   }
  
positive.code:   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;
    transportFile = pkgs.writeText "postfix-transport" cfg.transport;
  
  in
  
  
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 = "";
  