nixos/stalwart-mail: add module

nixos/modules/module-list.nix

@@ -594,6 +594,7 @@
   ./services/mail/rss2email.nix
   ./services/mail/schleuder.nix
   ./services/mail/spamassassin.nix
+  ./services/mail/stalwart-mail.nix
   ./services/mail/sympa.nix
   ./services/mail/zeyple.nix
   ./services/matrix/appservice-discord.nix

nixos/modules/services/mail/stalwart-mail.nix

@@ -0,0 +1,106 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.stalwart-mail;
+  configFormat = pkgs.formats.toml { };
+  configFile = configFormat.generate "stalwart-mail.toml" cfg.settings;
+  dataDir = "/var/lib/stalwart-mail";
+
+in {
+  options.services.stalwart-mail = {
+    enable = mkEnableOption (mdDoc "the Stalwart all-in-one email server");
+    package = mkPackageOptionMD pkgs "stalwart-mail" { };
+
+    settings = mkOption {
+      inherit (configFormat) type;
+      default = { };
+      description = mdDoc ''
+        Configuration options for the Stalwart email server.
+        See <https://stalw.art/docs/> for available options.
+
+        By default, the module is configured to store everything locally.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # Default config: all local
+    services.stalwart-mail.settings = {
+      global.tracing.method = mkDefault "stdout";
+      global.tracing.level = mkDefault "info";
+      queue.path = mkDefault "${dataDir}/queue";
+      report.path = mkDefault "${dataDir}/reports";
+      store.db.path = mkDefault "${dataDir}/data/index.sqlite3";
+      store.blob.type = mkDefault "local";
+      store.blob.local.path = mkDefault "${dataDir}/data/blobs";
+      resolver.type = mkDefault "system";
+    };
+
+    systemd.services.stalwart-mail = {
+      wantedBy = [ "multi-user.target" ];
+      after = [ "local-fs.target" "network.target" ];
+
+      preStart = ''
+        mkdir -p ${dataDir}/{queue,reports,data/blobs}
+      '';
+
+      serviceConfig = {
+        ExecStart =
+          "${cfg.package}/bin/stalwart-mail --config=${configFile}";
+
+        # Base from template resources/systemd/stalwart-mail.service
+        Type = "simple";
+        LimitNOFILE = 65536;
+        KillMode = "process";
+        KillSignal = "SIGINT";
+        Restart = "on-failure";
+        RestartSec = 5;
+        StandardOutput = "syslog";
+        StandardError = "syslog";
+        SyslogIdentifier = "stalwart-mail";
+
+        DynamicUser = true;
+        User = "stalwart-mail";
+        StateDirectory = "stalwart-mail";
+
+        # Bind standard privileged ports
+        AmbientCapabilities = [ "CAP_NET_BIND_SERVICE" ];
+        CapabilityBoundingSet = [ "CAP_NET_BIND_SERVICE" ];
+
+        # Hardening
+        DeviceAllow = [ "" ];
+        LockPersonality = true;
+        MemoryDenyWriteExecute = true;
+        PrivateDevices = true;
+        PrivateUsers = false;  # incompatible with CAP_NET_BIND_SERVICE
+        ProcSubset = "pid";
+        PrivateTmp = true;
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectProc = "invisible";
+        ProtectSystem = "strict";
+        RestrictAddressFamilies = [ "AF_INET" "AF_INET6" ];
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = [ "@system-service" "~@privileged" ];
+        UMask = "0077";
+      };
+    };
+
+    # Make admin commands available in the shell
+    environment.systemPackages = [ cfg.package ];
+  };
+
+  meta = {
+    maintainers = with maintainers; [ happysalada pacien ];
+  };
+}