/**
 * Extracts the domain portion from an email address.
 *
 * Uses `lastIndexOf("@")` to handle quoted `@` in the local part
 * without regex — no ReDoS risk.
 *
 * @returns The lowercased domain, or `null` if the input is not a
 *          structurally valid email address.
 */
export declare function extractDomain(email: string): string | null;
//# sourceMappingURL=utils.d.ts.map