$mail->isSMTP();                                      // Set mailer to use SMTP
    $mail->Host = 'smtp1.example.com;smtp2.example.com';  // Specify main and backup SMTP servers
    $mail->SMTPAuth = true;                               // Enable SMTP authentication
    $mail->Username = 'user@example.com';                 // SMTP username
    $mail->Password = 'secret';                           // SMTP password
    $mail->SMTPSecure = 'tls';                            // Enable TLS encryption, `ssl` also accepted
    $mail->Port = 587;