{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
  ];
}