SMTP 설정을 했는데 메일 보내기가 안됩니다

$mail = new PHPMailer(); // defaults to using php "mail()"
    /*
    if (defined('G5_SMTP') && G5_SMTP) {
        $mail->IsSMTP(); // telling the class to use SMTP
        $mail->Host = G5_SMTP; // SMTP server
        if(defined('G5_SMTP_PORT') && G5_SMTP_PORT)
            $mail->Port = G5_SMTP_PORT;
    }
    */
    $mail->IsSMTP();
    $mail->SMTPSecure = "ssl";
    $mail->SMTPAuth = true;
    $mail->Host = "smtp.gmail.com";
    $mail->Port = 465;
    $mail->Username = "1234@gmail.com";
    $mail->Password = "1234";