/**
 * All platforms Email classes should implement this base class
 */
declare abstract class Base_email<O> {
    protected opt: O | Partial<O>;
    /**
     * Default options
     *
     * new options should merge with it.
     */
    def: O | Partial<O>;
    /**
     * @param opt Could option like region, key and secret etc.
     */
    constructor(opt: O | Partial<O>);
    /**
     * Send email
     * @param from - from address
     * @param to - to address
     * @param subject - title
     * @param content - content
     * @param opt - send options
     */
    abstract send(from: string, to: string, subject: string, content: string, opt: any): Promise<any> | any;
    /**
     * Verify this.opt
     *
     * throws if invalid
     */
    abstract validate_opt(): true;
}

export { Base_email };