/**
 * Options for configuring email validation constraints.
 * All lengths are in characters and follow RFC 5321/5322 specifications.
 */
export interface IsEmailOptions {
    /**
     * Maximum total length of the email address (local part + @ + domain).
     * RFC 5321 recommends a maximum of 320 characters for SMTP.
     * @default 320
     */
    maxTotalLength?: number;
    /**
     * Maximum length of the local part (before @).
     * RFC 5321 specifies a maximum of 64 characters for the local part.
     * @default 64
     */
    maxLocalPartLength?: number;
    /**
     * Maximum length of the domain part (after @).
     * RFC 1035 specifies a maximum of 255 characters for domain names.
     * @default 255
     */
    maxDomainLength?: number;
    /**
     * Maximum length of individual domain labels (parts separated by dots).
     * RFC 1035 specifies a maximum of 63 characters per label.
     * @default 63
     */
    maxDomainLabelLength?: number;
}
/**
 * Validates whether a given string is a valid email address.
 *
 * This function performs comprehensive email validation according to RFC 5322 standards,
 * handling all edge cases including:
 * - Local part validation (before @): allows letters, numbers, and special chars like .!#$%&'*+-/=?^_`{|}~
 * - Quoted strings in local part (e.g., "john..doe"@example.com)
 * - Domain validation: proper domain structure with valid TLD
 * - IP address domains: [IPv4] and [IPv6] formats
 * - International domains: IDN (Internationalized Domain Names)
 * - Configurable length constraints with sensible defaults
 * - Edge cases: consecutive dots, leading/trailing dots, escaped characters
 *
 * @param email - The string to validate as an email address
 * @param options - Optional configuration for validation constraints
 * @returns true if the string is a valid email address, false otherwise
 *
 * @example
 * isEmail("user@example.com") // true
 * isEmail("user.name+tag@example.co.uk") // true
 * isEmail("invalid@") // false
 * isEmail("@invalid.com") // false
 *
 * // Custom length limits
 * isEmail("very.long.email@domain.com", { maxTotalLength: 100 }) // true if under 100 chars
 */
export declare function isEmail(email: unknown, options?: IsEmailOptions): boolean;