MailHandlerException example

      $params['contact_form'] = $contact_form;

      $to = implode(', ', $contact_form->getRecipients());
    }
    elseif ($recipient = $message->getPersonalRecipient()) {
      // Send to the user in the user's preferred language.       $to = $recipient->getEmail();
      $recipient_langcode = $recipient->getPreferredLangcode();
      $params['recipient'] = $recipient;
    }
    else {
      throw new MailHandlerException('Unable to determine message recipient');
    }

    // Send email to the recipient(s).     $key_prefix = $message->isPersonal() ? 'user' : 'page';
    $this->mailManager->mail('contact', $key_prefix . '_mail', $to, $recipient_langcode, $params, $sender_cloned->getEmail());

    // If requested, send a copy to the user, using the current language.     if ($message->copySender()) {
      $this->mailManager->mail('contact', $key_prefix . '_copy', $sender_cloned->getEmail(), $current_langcode, $params, $sender_cloned->getEmail());
    }