/**
 * Normalize (trim + lowercase) and validate an email address.
 *
 * Returns the normalized email when valid, or `null` when the input is missing,
 * empty, or fails validation.
 *
 * This frontend check must be equal to or *less* restrictive than
 * the backend.
 */
export declare function normalizeAndValidateEmail(email: string | undefined | null): string | null;
/** Boolean predicate built on the same normalization as `normalizeAndValidateEmail`. */
export declare function isValidEmail(email: string | undefined | null): boolean;
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