Magento – Magento 2.2.6 Change ‘From’ field of magento contact form email to the sender

Currently, when customer submit a contact form through our website, the "sent from" email address we received is our support@example.com. I would like to change the "send from" email address to be the email address the customer entered in the contact form. how do i achieve that in magento 2.2.6?

There is an solution to magento 1 here, but i can't find the same file to edit for magento2. https://stackoverflow.com/questions/6188855/change-from-field-of-magento-contact-form-email-to-the-sender

my index.php file looks like this

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Contact\Controller;

use Magento\Contact\Model\ConfigInterface;
use Magento\Framework\App\Action\Context;
use Magento\Framework\App\RequestInterface;
use Magento\Framework\Exception\NotFoundException;

/**
 * Contact module base controller
 */
abstract class Index extends \Magento\Framework\App\Action\Action
{
    /**
     * Recipient email config path
     */
    const XML_PATH_EMAIL_RECIPIENT = ConfigInterface::XML_PATH_EMAIL_RECIPIENT;

    /**
     * Sender email config path
     */
    const XML_PATH_EMAIL_SENDER = ConfigInterface::XML_PATH_EMAIL_SENDER; /* i would like to make the sender to be customer's email address here*/

    /**
     * Email template config path
     */
    const XML_PATH_EMAIL_TEMPLATE = ConfigInterface::XML_PATH_EMAIL_TEMPLATE;

    /**
     * Enabled config path
     */
    const XML_PATH_ENABLED = ConfigInterface::XML_PATH_ENABLED;

    /**
     * @var ConfigInterface
     */
    private $contactsConfig;

    /**
     * @param Context $context
     * @param ConfigInterface $contactsConfig
     */
    public function __construct(
        Context $context,
        ConfigInterface $contactsConfig
    ) {
        parent::__construct($context);
        $this->contactsConfig = $contactsConfig;
    }

    /**
     * Dispatch request
     *
     * @param RequestInterface $request
     * @return \Magento\Framework\App\ResponseInterface
     * @throws \Magento\Framework\Exception\NotFoundException
     */
    public function dispatch(RequestInterface $request)
    {
        if (!$this->contactsConfig->isEnabled()) {
            throw new NotFoundException(__('Page not found.'));
        }
        return parent::dispatch($request);
    }
}

It's an issue with our help desk system, because the help desk ticket will created it using the "sent from" email address, thus all ticket are created with customer "support@example.com"

I'm thinking within …../Contact/Controller/Index/Post.php should be able to achieve that.

/**
 *
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Contact\Controller\Index;
use Magento\Contact\Model\ConfigInterface;
use Magento\Contact\Model\MailInterface;
use Magento\Framework\App\Action\Context;
use Magento\Framework\App\Request\DataPersistorInterface;
use Magento\Framework\Controller\Result\Redirect;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\HTTP\PhpEnvironment\Request;
use Psr\Log\LoggerInterface;
use Magento\Framework\App\ObjectManager;
use Magento\Framework\DataObject;
class Post extends \Magento\Contact\Controller\Index
{
    /**
     * @var DataPersistorInterface
     */
    private $dataPersistor;
    /**
     * @var Context
     */
    private $context;
    /**
     * @var MailInterface
     */
    private $mail;
    /**
     * @var LoggerInterface
     */
    private $logger;
    /**
     * @param Context $context
     * @param ConfigInterface $contactsConfig
     * @param MailInterface $mail
     * @param DataPersistorInterface $dataPersistor
     * @param LoggerInterface $logger
     */
    public function __construct(
        Context $context,
        ConfigInterface $contactsConfig,
        MailInterface $mail,
        DataPersistorInterface $dataPersistor,
        LoggerInterface $logger = null
    ) {
        parent::__construct($context, $contactsConfig);
        $this->context = $context;
        $this->mail = $mail;
        $this->dataPersistor = $dataPersistor;
        $this->logger = $logger ?: ObjectManager::getInstance()->get(LoggerInterface::class);
    }
    /**
     * Post user question
     *
     * @return Redirect
     */
    public function execute()
    {
        if (!$this->isPostRequest()) {
            return $this->resultRedirectFactory->create()->setPath('*/*/');
        }
        try {
            $this->sendEmail($this->validatedParams());
            $this->messageManager->addSuccessMessage(
                __('Thanks for contacting us with your comments and questions. We\'ll respond to you very soon.')
            );
            $this->dataPersistor->clear('contact_us');
        } catch (LocalizedException $e) {
            $this->messageManager->addErrorMessage($e->getMessage());
            $this->dataPersistor->set('contact_us', $this->getRequest()->getParams());
        } catch (\Exception $e) {
            $this->logger->critical($e);
            $this->messageManager->addErrorMessage(
                __('An error occurred while processing your form. Please try again later.')
            );
            $this->dataPersistor->set('contact_us', $this->getRequest()->getParams());
        }
        return $this->resultRedirectFactory->create()->setPath('contact/index');
    }
    /**
     * @param array $post Post data from contact form
     * @return void
     */
    private function sendEmail($post)
    {
        $this->mail->send(
            $post['email'],
            ['data' => new DataObject($post)]
        );
    }
    /**
     * @return bool
     */
    private function isPostRequest()
    {
        /** @var Request $request */
        $request = $this->getRequest();
        return !empty($request->getPostValue());
    }
    /**
     * @return array
     * @throws \Exception
     */
    private function validatedParams()
    {
        $request = $this->getRequest();
        if (trim($request->getParam('name')) === '') {
            throw new LocalizedException(__('Name is missing'));
        }
        if (trim($request->getParam('comment')) === '') {
            throw new LocalizedException(__('Comment is missing'));
        }
        if (false === \strpos($request->getParam('email'), '@')) {
            throw new LocalizedException(__('Invalid email address'));
        }
        if (trim($request->getParam('hideit')) !== '') {
            throw new \Exception();
        }
        return $request->getParams();
    }
}