mailsystem: Add nginx configuration to retrieve letsencrypt certificate

mailsystem/default.nix

@@ -0,0 +1,21 @@
+{lib, ...}: {
+  options.mailsystem = {
+    enable = lib.mkEnableOption "nixos-mailsystem";
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Automatically open ports in the firewall.";
+    };
+
+    fqdn = lib.mkOption {
+      type = lib.types.str;
+      example = "mail.example.com";
+      description = "Fully qualified domain name of the mail server.";
+    };
+  };
+
+  imports = [
+    ./nginx.nix
+  ];
+}