nixos/mailcatcher: init module for existing package

nixos/modules/module-list.nix

@@ -349,6 +349,7 @@
   ./services/mail/exim.nix
   ./services/mail/freepops.nix
   ./services/mail/mail.nix
+  ./services/mail/mailcatcher.nix
   ./services/mail/mailhog.nix
   ./services/mail/mlmmj.nix
   ./services/mail/offlineimap.nix

nixos/modules/services/mail/mailcatcher.nix

@@ -0,0 +1,60 @@
+{ config, pkgs, lib, ... }:
+
+let
+  cfg = config.services.mailcatcher;
+
+  inherit (lib) mkEnableOption mkIf mkOption types;
+in
+{
+  # interface
+
+  options = {
+
+    services.mailcatcher = {
+      enable = mkEnableOption "Enable MailCatcher.";
+
+      http.ip = mkOption {
+        type = types.str;
+        default = "127.0.0.1";
+        description = "The ip address of the http server.";
+      };
+
+      http.port = mkOption {
+        type = types.port;
+        default = 1080;
+        description = "The port address of the http server.";
+      };
+
+      smtp.ip = mkOption {
+        type = types.str;
+        default = "127.0.0.1";
+        description = "The ip address of the smtp server.";
+      };
+
+      smtp.port = mkOption {
+        type = types.port;
+        default = 1025;
+        description = "The port address of the smtp server.";
+      };
+    };
+
+  };
+
+  # implementation
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = [ pkgs.mailcatcher ];
+
+    systemd.services.mailcatcher = {
+      description = "MailCatcher Service";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        DynamicUser = true;
+        Restart = "always";
+        ExecStart = "${pkgs.mailcatcher}/bin/mailcatcher --foreground --no-quit --http-ip ${cfg.http.ip} --http-port ${toString cfg.http.port} --smtp-ip ${cfg.smtp.ip} --smtp-port ${toString cfg.smtp.port}";
+      };
+    };
+  };
+}