/**
 * Browser twin of net.ts (swapped in via the package.json "browser" field).
 *
 * MX verification via Cloudflare's DNS-over-HTTPS JSON API. Privacy note:
 * only the bare domain is transmitted — never the full email address — and
 * it goes to a DNS resolver, which is where domain lookups go anyway.
 * Failures, timeouts, and rate limits all degrade to "no MX", matching the
 * Node implementation's behaviour.
 */
export declare function hasMxRecord(domain: string): Promise<boolean>;