1 files changed, 61 insertions, 0 deletions
diff --git a/ops/modules/smtprelay.nix b/ops/modules/smtprelay.nix
new file mode 100644
index 000000000000..f6ce2621757d
--- /dev/null
+++ b/ops/modules/smtprelay.nix
@@ -0,0 +1,61 @@
+# NixOS module for configuring the simple SMTP relay.
+{ depot, pkgs, config, lib, ... }:
+
+let
+  inherit (builtins) attrValues mapAttrs;
+  inherit (lib)
+    concatStringsSep
+    mkEnableOption
+    mkIf
+    mkOption
+    types
+    ;
+
+  cfg = config.services.depot.smtprelay;
+  description = "Simple SMTP relay";
+
+  # Configuration values that are always overridden.
+  #
+  # - logging is pinned to stdout for journald compatibility
+  # - secret config is loaded through systemd's credential loading facility
+  overrideArgs = {
+    logfile = "";
+    config = "$CREDENTIALS_DIRECTORY/secrets";
+  };
+
+  # Creates the command line argument string for the service.
+  prepareArgs = args:
+    concatStringsSep " "
+      (attrValues (mapAttrs (key: value: "-${key} \"${toString value}\"")
+        (args // overrideArgs)));
+in
+{
+  options.services.depot.smtprelay = {
+    enable = mkEnableOption description;
+
+    args = mkOption {
+      type = types.attrsOf types.str;
+      description = "Key value pairs for command line arguments";
+    };
+
+    secretsFile = mkOption {
+      type = types.str;
+      default = config.age.secretsDir + "/smtprelay";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.smtprelay = {
+      inherit description;
+      script = "${depot.third_party.smtprelay}/bin/smtprelay ${prepareArgs cfg.args}";
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        Restart = "always";
+        StateDirectory = "smtprelay";
+        DynamicUser = true;
+        LoadCredential = "secrets:${cfg.secretsFile}";
+      };
+    };
+  };
+}