{ config, lib, pkgs, ... }:
let

  cfg = config.services.postfix;
  user = cfg.user;
  group = cfg.group;
  setgidGroup = cfg.setgidGroup;

  haveAliases = cfg.postmasterAlias != "" || cfg.rootAlias != ""
                      || cfg.extraAliases != "";
  haveCanonical = cfg.canonical != "";
  haveTransport = cfg.transport != "";
  haveVirtual = cfg.virtual != "";
  haveLocalRecipients = cfg.localRecipients != null;

  clientAccess =
    lib.optional (cfg.dnsBlacklistOverrides != "")
      "check_client_access hash:/etc/postfix/client_access";

  dnsBl =
    lib.optionals (cfg.dnsBlacklists != [])
      (map (s: "reject_rbl_client " + s) cfg.dnsBlacklists);

  clientRestrictions = lib.concatStringsSep ", " (clientAccess ++ dnsBl);

  mainCf = let
    escape = lib.replaceStrings ["$"] ["$$"];
    mkList = items: "\n  " + lib.concatStringsSep ",\n  " items;
    mkVal = value:
      if lib.isList value then mkList value
        else " " + (if value == true then "yes"
        else if value == false then "no"
        else toString value);
    mkEntry = name: value: "${escape name} =${mkVal value}";
  in
    lib.concatStringsSep "\n" (lib.mapAttrsToList mkEntry cfg.config)
      + "\n" + cfg.extraConfig;

  masterCfOptions = { options, config, name, ... }: {
    options = {
      name = lib.mkOption {
        type = lib.types.str;
        default = name;
        example = "smtp";
        description = ''
          The name of the service to run. Defaults to the attribute set key.
        '';
      };

      type = lib.mkOption {
        type = lib.types.enum [ "inet" "unix" "unix-dgram" "fifo" "pass" ];
        default = "unix";
        example = "inet";
        description = "The type of the service";
      };

      private = lib.mkOption {
        type = lib.types.bool;
        example = false;
        description = ''
          Whether the service's sockets and storage directory is restricted to
          be only available via the mail system. If `null` is
          given it uses the postfix default `true`.
        '';
      };

      privileged = lib.mkOption {
        type = lib.types.bool;
        example = true;
        description = "";
      };

      chroot = lib.mkOption {
        type = lib.types.bool;
        example = true;
        description = ''
          Whether the service is chrooted to have only access to the
          {option}`services.postfix.queueDir` and the closure of
          store paths specified by the {option}`program` option.
        '';
      };

      wakeup = lib.mkOption {
        type = lib.types.int;
        example = 60;
        description = ''
          Automatically wake up the service after the specified number of
          seconds. If `0` is given, never wake the service
          up.
        '';
      };

      wakeupUnusedComponent = lib.mkOption {
        type = lib.types.bool;
        example = false;
        description = ''
          If set to `false` the component will only be woken
          up if it is used. This is equivalent to postfix' notion of adding a
          question mark behind the wakeup time in
          {file}`master.cf`
        '';
      };

      maxproc = lib.mkOption {
        type = lib.types.int;
        example = 1;
        description = ''
          The maximum number of processes to spawn for this service. If the
          value is `0` it doesn't have any limit. If
          `null` is given it uses the postfix default of
          `100`.
        '';
      };

      command = lib.mkOption {
        type = lib.types.str;
        default = name;
        example = "smtpd";
        description = ''
          A program name specifying a Postfix service/daemon process.
          By default it's the attribute {option}`name`.
        '';
      };

      args = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        default = [];
        example = [ "-o" "smtp_helo_timeout=5" ];
        description = ''
          Arguments to pass to the {option}`command`. There is no shell
          processing involved and shell syntax is passed verbatim to the
          process.
        '';
      };

      rawEntry = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        default = [];
        internal = true;
        description = ''
          The raw configuration line for the {file}`master.cf`.
        '';
      };
    };

    config.rawEntry = let
      mkBool = bool: if bool then "y" else "n";
      mkArg = arg: "${lib.optionalString (lib.hasPrefix "-" arg) "\n  "}${arg}";

      maybeOption = fun: option:
        if options.${option}.isDefined then fun config.${option} else "-";

      # This is special, because we have two options for this value.
      wakeup = let
        wakeupDefined = options.wakeup.isDefined;
        wakeupUCDefined = options.wakeupUnusedComponent.isDefined;
        finalValue = toString config.wakeup
                   + lib.optionalString (wakeupUCDefined && !config.wakeupUnusedComponent) "?";
      in if wakeupDefined then finalValue else "-";

    in [
      config.name
      config.type
      (maybeOption mkBool "private")
      (maybeOption (b: mkBool (!b)) "privileged")
      (maybeOption mkBool "chroot")
      wakeup
      (maybeOption toString "maxproc")
      (config.command + " " + lib.concatMapStringsSep " " mkArg config.args)
    ];
  };

  masterCfContent = let

    labels = [
      "# service" "type" "private" "unpriv" "chroot" "wakeup" "maxproc"
      "command + args"
    ];

    labelDefaults = [
      "# " "" "(yes)" "(yes)" "(no)" "(never)" "(100)" "" ""
    ];

    masterCf = lib.mapAttrsToList (lib.const (lib.getAttr "rawEntry")) cfg.masterConfig;

    # A list of the maximum width of the columns across all lines and labels
    maxWidths = let
      foldLine = line: acc: let
        columnLengths = map lib.stringLength line;
      in lib.zipListsWith lib.max acc columnLengths;
      # We need to handle the last column specially here, because it's
      # open-ended (command + args).
      lines = [ labels labelDefaults ] ++ (map (l: lib.init l ++ [""]) masterCf);
    in lib.foldr foldLine (lib.genList (lib.const 0) (lib.length labels)) lines;

    # Pad a string with spaces from the right (opposite of fixedWidthString).
    pad = width: str: let
      padWidth = width - lib.stringLength str;
      padding = lib.concatStrings (lib.genList (lib.const " ") padWidth);
    in str + lib.optionalString (padWidth > 0) padding;

    # It's + 2 here, because that's the amount of spacing between columns.
    fullWidth = lib.foldr (width: acc: acc + width + 2) 0 maxWidths;

    formatLine = line: lib.concatStringsSep "  " (lib.zipListsWith pad maxWidths line);

    formattedLabels = let
      sep = "# " + lib.concatStrings (lib.genList (lib.const "=") (fullWidth + 5));
      lines = [ sep (formatLine labels) (formatLine labelDefaults) sep ];
    in lib.concatStringsSep "\n" lines;

  in formattedLabels + "\n" + lib.concatMapStringsSep "\n" formatLine masterCf + "\n" + cfg.extraMasterConf;

  headerCheckOptions = { ... }:
  {
    options = {
      pattern = lib.mkOption {
        type = lib.types.str;
        default = "/^.*/";
        example = "/^X-Mailer:/";
        description = "A regexp pattern matching the header";
      };
      action = lib.mkOption {
        type = lib.types.str;
        default = "DUNNO";
        example = "BCC mail@example.com";
        description = "The action to be executed when the pattern is matched";
      };
    };
  };

  headerChecks = lib.concatStringsSep "\n" (map (x: "${x.pattern} ${x.action}") cfg.headerChecks) + cfg.extraHeaderChecks;

  aliases = let separator = lib.optionalString (cfg.aliasMapType == "hash") ":"; in
    lib.optionalString (cfg.postmasterAlias != "") ''
      postmaster${separator} ${cfg.postmasterAlias}
    ''
    + lib.optionalString (cfg.rootAlias != "") ''
      root${separator} ${cfg.rootAlias}
    ''
    + cfg.extraAliases
  ;

  aliasesFile = pkgs.writeText "postfix-aliases" aliases;
  canonicalFile = pkgs.writeText "postfix-canonical" cfg.canonical;
  virtualFile = pkgs.writeText "postfix-virtual" cfg.virtual;
  localRecipientMapFile = pkgs.writeText "postfix-local-recipient-map" (lib.concatMapStrings (x: x + " ACCEPT\n") cfg.localRecipients);
  checkClientAccessFile = pkgs.writeText "postfix-check-client-access" cfg.dnsBlacklistOverrides;
  mainCfFile = pkgs.writeText "postfix-main.cf" mainCf;
  masterCfFile = pkgs.writeText "postfix-master.cf" masterCfContent;
  transportFile = pkgs.writeText "postfix-transport" cfg.transport;
  headerChecksFile = pkgs.writeText "postfix-header-checks" headerChecks;

in

{

  ###### interface

  options = {

    services.postfix = {

      enable = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to run the Postfix mail server.";
      };

      enableSmtp = lib.mkOption {
        type = lib.types.bool;
        default = true;
        description = "Whether to enable smtp in master.cf.";
      };

      enableSubmission = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to enable smtp submission.";
      };

      enableSubmissions = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = ''
          Whether to enable smtp submission via smtps.

          According to RFC 8314 this should be preferred
          over STARTTLS for submission of messages by end user clients.
        '';
      };

      submissionOptions = lib.mkOption {
        type = with lib.types; attrsOf str;
        default = {
          smtpd_tls_security_level = "encrypt";
          smtpd_sasl_auth_enable = "yes";
          smtpd_client_restrictions = "permit_sasl_authenticated,reject";
          milter_macro_daemon_name = "ORIGINATING";
        };
        example = {
          smtpd_tls_security_level = "encrypt";
          smtpd_sasl_auth_enable = "yes";
          smtpd_sasl_type = "dovecot";
          smtpd_client_restrictions = "permit_sasl_authenticated,reject";
          milter_macro_daemon_name = "ORIGINATING";
        };
        description = "Options for the submission config in master.cf";
      };

      submissionsOptions = lib.mkOption {
        type = with lib.types; attrsOf str;
        default = {
          smtpd_sasl_auth_enable = "yes";
          smtpd_client_restrictions = "permit_sasl_authenticated,reject";
          milter_macro_daemon_name = "ORIGINATING";
        };
        example = {
          smtpd_sasl_auth_enable = "yes";
          smtpd_sasl_type = "dovecot";
          smtpd_client_restrictions = "permit_sasl_authenticated,reject";
          milter_macro_daemon_name = "ORIGINATING";
        };
        description = ''
          Options for the submission config via smtps in master.cf.

          smtpd_tls_security_level will be set to encrypt, if it is missing
          or has one of the values "may" or "none".

          smtpd_tls_wrappermode with value "yes" will be added automatically.
        '';
      };

      setSendmail = lib.mkOption {
        type = lib.types.bool;
        default = true;
        description = "Whether to set the system sendmail to postfix's.";
      };

      user = lib.mkOption {
        type = lib.types.str;
        default = "postfix";
        description = "What to call the Postfix user (must be used only for postfix).";
      };

      group = lib.mkOption {
        type = lib.types.str;
        default = "postfix";
        description = "What to call the Postfix group (must be used only for postfix).";
      };

      setgidGroup = lib.mkOption {
        type = lib.types.str;
        default = "postdrop";
        description = ''
          How to call postfix setgid group (for postdrop). Should
          be uniquely used group.
        '';
      };

      networks = lib.mkOption {
        type = lib.types.nullOr (lib.types.listOf lib.types.str);
        default = null;
        example = ["192.168.0.1/24"];
        description = ''
          Net masks for trusted - allowed to relay mail to third parties -
          hosts. Leave empty to use mynetworks_style configuration or use
          default (localhost-only).
        '';
      };

      networksStyle = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Name of standard way of trusted network specification to use,
          leave blank if you specify it explicitly or if you want to use
          default (localhost-only).
        '';
      };

      hostname = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Hostname to use. Leave blank to use just the hostname of machine.
          It should be FQDN.
        '';
      };

      domain = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Domain to use. Leave blank to use hostname minus first component.
        '';
      };

      origin = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Origin to use in outgoing e-mail. Leave blank to use hostname.
        '';
      };

      destination = lib.mkOption {
        type = lib.types.nullOr (lib.types.listOf lib.types.str);
        default = null;
        example = ["localhost"];
        description = ''
          Full (!) list of domains we deliver locally. Leave blank for
          acceptable Postfix default.
        '';
      };

      relayDomains = lib.mkOption {
        type = lib.types.nullOr (lib.types.listOf lib.types.str);
        default = null;
        example = ["localdomain"];
        description = ''
          List of domains we agree to relay to. Default is empty.
        '';
      };

      relayHost = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Mail relay for outbound mail.
        '';
      };

      relayPort = lib.mkOption {
        type = lib.types.int;
        default = 25;
        description = ''
          SMTP port for relay mail relay.
        '';
      };

      lookupMX = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = ''
          Whether relay specified is just domain whose MX must be used.
        '';
      };

      postmasterAlias = lib.mkOption {
        type = lib.types.str;
        default = "root";
        description = ''
          Who should receive postmaster e-mail. Multiple values can be added by
          separating values with comma.
        '';
      };

      rootAlias = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = ''
          Who should receive root e-mail. Blank for no redirection.
          Multiple values can be added by separating values with comma.
        '';
      };

      extraAliases = lib.mkOption {
        type = lib.types.lines;
        default = "";
        description = ''
          Additional entries to put verbatim into aliases file, cf. man-page aliases(8).
        '';
      };

      aliasMapType = lib.mkOption {
        type = with lib.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 = lib.mkOption {
        type = with lib.types; attrsOf (oneOf [ bool int str (listOf str) ]);
        description = ''
          The main.cf configuration file as key value set.
        '';
        example = {
          mail_owner = "postfix";
          smtp_tls_security_level = "may";
        };
      };

      extraConfig = lib.mkOption {
        type = lib.types.lines;
        default = "";
        description = ''
          Extra lines to be added verbatim to the main.cf configuration file.
        '';
      };

      tlsTrustedAuthorities = lib.mkOption {
        type = lib.types.str;
        default = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";
        defaultText = lib.literalExpression ''"''${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt"'';
        description = ''
          File containing trusted certification authorities (CA) to verify certificates of mailservers contacted for mail delivery. This basically sets smtp_tls_CAfile and enables opportunistic tls. Defaults to NixOS trusted certification authorities.
        '';
      };

      sslCert = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = "SSL certificate to use.";
      };

      sslKey = lib.mkOption {
        type = lib.types.str;
        default = "";
        description = "SSL key to use.";
      };

      recipientDelimiter = lib.mkOption {
        type = lib.types.str;
        default = "";
        example = "+";
        description = ''
          Delimiter for address extension: so mail to user+test can be handled by ~user/.forward+test
        '';
      };

      canonical = lib.mkOption {
        type = lib.types.lines;
        default = "";
        description = ''
          Entries for the {manpage}`canonical(5)` table.
        '';
      };

      virtual = lib.mkOption {
        type = lib.types.lines;
        default = "";
        description = ''
          Entries for the virtual alias map, cf. man-page virtual(5).
        '';
      };

      virtualMapType = lib.mkOption {
        type = lib.types.enum ["hash" "regexp" "pcre"];
        default = "hash";
        description = ''
          What type of virtual alias map file to use. Use `"regexp"` for regular expressions.
        '';
      };

      localRecipients = lib.mkOption {
        type = with lib.types; nullOr (listOf str);
        default = null;
        description = ''
          List of accepted local users. Specify a bare username, an
          `"@domain.tld"` wild-card, or a complete
          `"user@domain.tld"` address. If set, these names end
          up in the local recipient map -- see the local(8) man-page -- and
          effectively replace the system user database lookup that's otherwise
          used by default.
        '';
      };

      transport = lib.mkOption {
        default = "";
        type = lib.types.lines;
        description = ''
          Entries for the transport map, cf. man-page transport(8).
        '';
      };

      dnsBlacklists = lib.mkOption {
        default = [];
        type = with lib.types; listOf str;
        description = "dns blacklist servers to use with smtpd_client_restrictions";
      };

      dnsBlacklistOverrides = lib.mkOption {
        default = "";
        type = lib.types.lines;
        description = "contents of check_client_access for overriding dnsBlacklists";
      };

      masterConfig = lib.mkOption {
        type = lib.types.attrsOf (lib.types.submodule masterCfOptions);
        default = {};
        example =
          { submission = {
              type = "inet";
              args = [ "-o" "smtpd_tls_security_level=encrypt" ];
            };
          };
        description = ''
          An attribute set of service options, which correspond to the service
          definitions usually done within the Postfix
          {file}`master.cf` file.
        '';
      };

      extraMasterConf = lib.mkOption {
        type = lib.types.lines;
        default = "";
        example = "submission inet n - n - - smtpd";
        description = "Extra lines to append to the generated master.cf file.";
      };

      enableHeaderChecks = lib.mkOption {
        type = lib.types.bool;
        default = false;
        example = true;
        description = "Whether to enable postfix header checks";
      };

      headerChecks = lib.mkOption {
        type = lib.types.listOf (lib.types.submodule headerCheckOptions);
        default = [];
        example = [ { pattern = "/^X-Spam-Flag:/"; action = "REDIRECT spam@example.com"; } ];
        description = "Postfix header checks.";
      };

      extraHeaderChecks = lib.mkOption {
        type = lib.types.lines;
        default = "";
        example = "/^X-Spam-Flag:/ REDIRECT spam@example.com";
        description = "Extra lines to /etc/postfix/header_checks file.";
      };

      aliasFiles = lib.mkOption {
        type = lib.types.attrsOf lib.types.path;
        default = {};
        description = "Aliases' tables to be compiled and placed into /var/lib/postfix/conf.";
      };

      mapFiles = lib.mkOption {
        type = lib.types.attrsOf lib.types.path;
        default = {};
        description = "Maps to be compiled and placed into /var/lib/postfix/conf.";
      };

      useSrs = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Whether to enable sender rewriting scheme";
      };

    };

  };


  ###### implementation

  config = lib.mkIf config.services.postfix.enable (lib.mkMerge [
    {

      environment = {
        etc.postfix.source = "/var/lib/postfix/conf";

        # This makes it comfortable to run 'postqueue/postdrop' for example.
        systemPackages = [ pkgs.postfix ];
      };

      services.pfix-srsd.enable = config.services.postfix.useSrs;

      services.mail.sendmailSetuidWrapper = lib.mkIf config.services.postfix.setSendmail {
        program = "sendmail";
        source = "${pkgs.postfix}/bin/sendmail";
        owner = "root";
        group = setgidGroup;
        setuid = false;
        setgid = true;
      };

      security.wrappers.mailq = {
        program = "mailq";
        source = "${pkgs.postfix}/bin/mailq";
        owner = "root";
        group = setgidGroup;
        setuid = false;
        setgid = true;
      };

      security.wrappers.postqueue = {
        program = "postqueue";
        source = "${pkgs.postfix}/bin/postqueue";
        owner = "root";
        group = setgidGroup;
        setuid = false;
        setgid = true;
      };

      security.wrappers.postdrop = {
        program = "postdrop";
        source = "${pkgs.postfix}/bin/postdrop";
        owner = "root";
        group = setgidGroup;
        setuid = false;
        setgid = true;
      };

      users.users = lib.optionalAttrs (user == "postfix")
        { postfix = {
            description = "Postfix mail server user";
            uid = config.ids.uids.postfix;
            group = group;
          };
        };

      users.groups =
        lib.optionalAttrs (group == "postfix")
        { ${group}.gid = config.ids.gids.postfix;
        }
        // lib.optionalAttrs (setgidGroup == "postdrop")
        { ${setgidGroup}.gid = config.ids.gids.postdrop;
        };

      systemd.services.postfix-setup =
        { description = "Setup for Postfix mail server";
          serviceConfig.RemainAfterExit = true;
          serviceConfig.Type = "oneshot";
          script = ''
            # Backwards compatibility
            if [ ! -d /var/lib/postfix ] && [ -d /var/postfix ]; then
              mkdir -p /var/lib
              mv /var/postfix /var/lib/postfix
            fi

            # All permissions set according ${pkgs.postfix}/etc/postfix/postfix-files script
            mkdir -p /var/lib/postfix /var/lib/postfix/queue/{pid,public,maildrop}
            chmod 0755 /var/lib/postfix
            chown root:root /var/lib/postfix

            rm -rf /var/lib/postfix/conf
            mkdir -p /var/lib/postfix/conf
            chmod 0755 /var/lib/postfix/conf
            ln -sf ${pkgs.postfix}/etc/postfix/postfix-files /var/lib/postfix/conf/postfix-files
            ln -sf ${mainCfFile} /var/lib/postfix/conf/main.cf
            ln -sf ${masterCfFile} /var/lib/postfix/conf/master.cf

            ${lib.concatStringsSep "\n" (lib.mapAttrsToList (to: from: ''
              ln -sf ${from} /var/lib/postfix/conf/${to}
              ${pkgs.postfix}/bin/postalias -o -p /var/lib/postfix/conf/${to}
            '') cfg.aliasFiles)}
            ${lib.concatStringsSep "\n" (lib.mapAttrsToList (to: from: ''
              ln -sf ${from} /var/lib/postfix/conf/${to}
              ${pkgs.postfix}/bin/postmap /var/lib/postfix/conf/${to}
            '') cfg.mapFiles)}

            mkdir -p /var/spool/mail
            chown root:root /var/spool/mail
            chmod a+rwxt /var/spool/mail
            ln -sf /var/spool/mail /var/

            #Finally delegate to postfix checking remain directories in /var/lib/postfix and set permissions on them
            ${pkgs.postfix}/bin/postfix set-permissions config_directory=/var/lib/postfix/conf
          '';
        };

      systemd.services.postfix =
        { description = "Postfix mail server";

          wantedBy = [ "multi-user.target" ];
          after = [ "network.target" "postfix-setup.service" ];
          requires = [ "postfix-setup.service" ];
          path = [ pkgs.postfix ];

          serviceConfig = {
            Type = "forking";
            Restart = "always";
            PIDFile = "/var/lib/postfix/queue/pid/master.pid";
            ExecStart = "${pkgs.postfix}/bin/postfix start";
            ExecStop = "${pkgs.postfix}/bin/postfix stop";
            ExecReload = "${pkgs.postfix}/bin/postfix reload";

            # Hardening
            PrivateTmp = true;
            PrivateDevices = true;
            ProtectSystem = "full";
            CapabilityBoundingSet = [ "~CAP_NET_ADMIN CAP_SYS_ADMIN CAP_SYS_BOOT CAP_SYS_MODULE" ];
            MemoryDenyWriteExecute = true;
            ProtectKernelModules = true;
            ProtectKernelTunables = true;
            ProtectControlGroups = true;
            RestrictAddressFamilies = [ "AF_INET" "AF_INET6" "AF_NETLINK" "AF_UNIX" ];
            RestrictNamespaces = true;
            RestrictRealtime = true;
          };
        };

      services.postfix.config = (lib.mapAttrs (_: v: lib.mkDefault v) {
        compatibility_level  = pkgs.postfix.version;
        mail_owner           = cfg.user;
        default_privs        = "nobody";

        # NixOS specific locations
        data_directory       = "/var/lib/postfix/data";
        queue_directory      = "/var/lib/postfix/queue";

        # Default location of everything in package
        meta_directory       = "${pkgs.postfix}/etc/postfix";
        command_directory    = "${pkgs.postfix}/bin";
        sample_directory     = "/etc/postfix";
        newaliases_path      = "${pkgs.postfix}/bin/newaliases";
        mailq_path           = "${pkgs.postfix}/bin/mailq";
        readme_directory     = false;
        sendmail_path        = "${pkgs.postfix}/bin/sendmail";
        daemon_directory     = "${pkgs.postfix}/libexec/postfix";
        manpage_directory    = "${pkgs.postfix}/share/man";
        html_directory       = "${pkgs.postfix}/share/postfix/doc/html";
        shlib_directory      = false;
        mail_spool_directory = "/var/spool/mail/";
        setgid_group         = cfg.setgidGroup;
      })
      // lib.optionalAttrs (cfg.relayHost != "") { relayhost = if cfg.lookupMX
                                                           then "${cfg.relayHost}:${toString cfg.relayPort}"
                                                           else "[${cfg.relayHost}]:${toString cfg.relayPort}"; }
      // lib.optionalAttrs (!config.networking.enableIPv6) { inet_protocols = lib.mkDefault "ipv4"; }
      // lib.optionalAttrs (cfg.networks != null) { mynetworks = cfg.networks; }
      // lib.optionalAttrs (cfg.networksStyle != "") { mynetworks_style = cfg.networksStyle; }
      // lib.optionalAttrs (cfg.hostname != "") { myhostname = cfg.hostname; }
      // lib.optionalAttrs (cfg.domain != "") { mydomain = cfg.domain; }
      // lib.optionalAttrs (cfg.origin != "") { myorigin =  cfg.origin; }
      // lib.optionalAttrs (cfg.destination != null) { mydestination = cfg.destination; }
      // lib.optionalAttrs (cfg.relayDomains != null) { relay_domains = cfg.relayDomains; }
      // lib.optionalAttrs (cfg.recipientDelimiter != "") { recipient_delimiter = cfg.recipientDelimiter; }
      // lib.optionalAttrs haveAliases { alias_maps = [ "${cfg.aliasMapType}:/etc/postfix/aliases" ]; }
      // lib.optionalAttrs haveTransport { transport_maps = [ "hash:/etc/postfix/transport" ]; }
      // lib.optionalAttrs haveVirtual { virtual_alias_maps = [ "${cfg.virtualMapType}:/etc/postfix/virtual" ]; }
      // lib.optionalAttrs haveLocalRecipients { local_recipient_maps = [ "hash:/etc/postfix/local_recipients" ] ++ lib.optional haveAliases "$alias_maps"; }
      // lib.optionalAttrs (cfg.dnsBlacklists != []) { smtpd_client_restrictions = clientRestrictions; }
      // lib.optionalAttrs cfg.useSrs {
        sender_canonical_maps = [ "tcp:127.0.0.1:10001" ];
        sender_canonical_classes = [ "envelope_sender" ];
        recipient_canonical_maps = [ "tcp:127.0.0.1:10002" ];
        recipient_canonical_classes = [ "envelope_recipient" ];
      }
      // lib.optionalAttrs cfg.enableHeaderChecks { header_checks = [ "regexp:/etc/postfix/header_checks" ]; }
      // lib.optionalAttrs (cfg.tlsTrustedAuthorities != "") {
        smtp_tls_CAfile = cfg.tlsTrustedAuthorities;
        smtp_tls_security_level = lib.mkDefault "may";
      }
      // lib.optionalAttrs (cfg.sslCert != "") {
        smtp_tls_cert_file = cfg.sslCert;
        smtp_tls_key_file = cfg.sslKey;

        smtp_tls_security_level = lib.mkDefault "may";

        smtpd_tls_cert_file = cfg.sslCert;
        smtpd_tls_key_file = cfg.sslKey;

        smtpd_tls_security_level = "may";
      };

      services.postfix.masterConfig = {
        pickup = {
          private = false;
          wakeup = 60;
          maxproc = 1;
        };
        cleanup = {
          private = false;
          maxproc = 0;
        };
        qmgr = {
          private = false;
          wakeup = 300;
          maxproc = 1;
        };
        tlsmgr = {
          wakeup = 1000;
          wakeupUnusedComponent = false;
          maxproc = 1;
        };
        rewrite = {
          command = "trivial-rewrite";
        };
        bounce = {
          maxproc = 0;
        };
        defer = {
          maxproc = 0;
          command = "bounce";
        };
        trace = {
          maxproc = 0;
          command = "bounce";
        };
        verify = {
          maxproc = 1;
        };
        flush = {
          private = false;
          wakeup = 1000;
          wakeupUnusedComponent = false;
          maxproc = 0;
        };
        proxymap = {
          command = "proxymap";
        };
        proxywrite = {
          maxproc = 1;
          command = "proxymap";
        };
        showq = {
          private = false;
        };
        error = {};
        retry = {
          command = "error";
        };
        discard = {};
        local = {
          privileged = true;
        };
        virtual = {
          privileged = true;
        };
        lmtp = {
        };
        anvil = {
          maxproc = 1;
        };
        scache = {
          maxproc = 1;
        };
      } // lib.optionalAttrs cfg.enableSubmission {
        submission = {
          type = "inet";
          private = false;
          command = "smtpd";
          args = let
            mkKeyVal = opt: val: [ "-o" (opt + "=" + val) ];
          in lib.concatLists (lib.mapAttrsToList mkKeyVal cfg.submissionOptions);
        };
      } // lib.optionalAttrs cfg.enableSmtp {
        smtp_inet = {
          name = "smtp";
          type = "inet";
          private = false;
          command = "smtpd";
        };
        smtp = {};
        relay = {
          command = "smtp";
          args = [ "-o" "smtp_fallback_relay=" ];
        };
      } // lib.optionalAttrs cfg.enableSubmissions {
        submissions = {
          type = "inet";
          private = false;
          command = "smtpd";
          args = let
            mkKeyVal = opt: val: [ "-o" (opt + "=" + val) ];
            adjustSmtpTlsSecurityLevel = !(cfg.submissionsOptions ? smtpd_tls_security_level) ||
                                      cfg.submissionsOptions.smtpd_tls_security_level == "none" ||
                                      cfg.submissionsOptions.smtpd_tls_security_level == "may";
            submissionsOptions = cfg.submissionsOptions // {
              smtpd_tls_wrappermode = "yes";
            } // lib.optionalAttrs adjustSmtpTlsSecurityLevel {
              smtpd_tls_security_level = "encrypt";
            };
          in lib.concatLists (lib.mapAttrsToList mkKeyVal submissionsOptions);
        };
      };
    }

    (lib.mkIf haveAliases {
      services.postfix.aliasFiles.aliases = aliasesFile;
    })
    (lib.mkIf haveCanonical {
      services.postfix.mapFiles.canonical = canonicalFile;
    })
    (lib.mkIf haveTransport {
      services.postfix.mapFiles.transport = transportFile;
    })
    (lib.mkIf haveVirtual {
      services.postfix.mapFiles.virtual = virtualFile;
    })
    (lib.mkIf haveLocalRecipients {
      services.postfix.mapFiles.local_recipients = localRecipientMapFile;
    })
    (lib.mkIf cfg.enableHeaderChecks {
      services.postfix.mapFiles.header_checks = headerChecksFile;
    })
    (lib.mkIf (cfg.dnsBlacklists != []) {
      services.postfix.mapFiles.client_access = checkClientAccessFile;
    })
  ]);

  imports = [
   (lib.mkRemovedOptionModule [ "services" "postfix" "sslCACert" ]
     "services.postfix.sslCACert was replaced by services.postfix.tlsTrustedAuthorities. In case you intend that your server should validate requested client certificates use services.postfix.extraConfig.")

   (lib.mkChangedOptionModule [ "services" "postfix" "useDane" ]
     [ "services" "postfix" "config" "smtp_tls_security_level" ]
     (config: lib.mkIf config.services.postfix.useDane "dane"))
  ];
}