/**
 * Simple check if argument is in e-mail format
 * @param {string} arg
 * @param {boolean} matches
 * @returns {boolean | string[] | null}
 *
 * ATTENTION: This function can cause a [Regular Expression Denial of Service (ReDoS)]:https://www.owasp.org/index.php/Regular_expression_Denial_of_Service_-_ReDoS
 */
export declare function isEmailFormat(arg: string, matches?: boolean): boolean | null | string[];