How to override default contact form Model file in Magento 2.2.5?

Question

I want to override default contact form Model file (ie, Mail.php and mailinterface.php) in Magento 2.
Struggling to override this file since the last 2days.
Any help would be appreciated.

/var/www/html/magento/app/code/Amy/Contactform/Model/Mail.php

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

use Magento\Framework\Mail\Template\TransportBuilder;
use Magento\Framework\Translate\Inline\StateInterface;
use Magento\Store\Model\StoreManagerInterface;
use Magento\Framework\App\ObjectManager;
use Magento\Framework\App\Area;

class Mail extends MailInterface
{
    /**
     * @var ConfigInterface
     */
    private $contactsConfig;

    /**
     * @var TransportBuilder
     */
    private $transportBuilder;

    /**
     * @var StateInterface
     */
    private $inlineTranslation;

    /**
     * @var StoreManagerInterface
     */
    private $storeManager;

    /**
     * Initialize dependencies.
     *
     * @param ConfigInterface $contactsConfig
     * @param TransportBuilder $transportBuilder
     * @param StateInterface $inlineTranslation
     * @param StoreManagerInterface|null $storeManager
     */
    public function __construct(
        ConfigInterface $contactsConfig,
        TransportBuilder $transportBuilder,
        StateInterface $inlineTranslation,
        StoreManagerInterface $storeManager = null
    ) {
        $this->contactsConfig = $contactsConfig;
        $this->transportBuilder = $transportBuilder;
        $this->inlineTranslation = $inlineTranslation;
        $this->storeManager = $storeManager ?: ObjectManager::getInstance()->get(StoreManagerInterface::class);
    }

    /**
     * Send email from contact form
     *
     * @param string $replyTo
     * @param array $variables
     * @return void
     */
    public function send($recipient, $replyTo, array $variables)
{
    /** @see \Magento\Contact\Controller\Index\Post::validatedParams() */
    $replyToName = !empty($variables['data']['name']) ? $variables['data']['name'] : null;
    if ($recipient == 'General feedback'){
        $emails = ['aaa@gmail.com'];  // add your email list
    }else if ($recipient == 'Warranty'){
        $emails = ['bbb@gmail.com'];  // add your email list 
    }

    $this->inlineTranslation->suspend();
    try {
        $transport = $this->transportBuilder
            ->setTemplateIdentifier($this->contactsConfig->emailTemplate())
            ->setTemplateOptions(
                [
                    'area' => Area::AREA_FRONTEND,
                    'store' => $this->storeManager->getStore()->getId()
                ]
            )
            ->setTemplateVars($variables)
            ->setFrom($this->contactsConfig->emailSender())
            ->addTo($emails)
            ->setReplyTo($replyTo, $replyToName)
            ->getTransport();

        $transport->sendMessage();
    } finally {
        $this->inlineTranslation->resume();
    }
}
}

/var/www/html/magento/app/code/Amy/Contactform/Model/Mail1Interface.php

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

/**
 * Email from contact form
 *
 * @api
 * @since 100.2.0
 */
interface Mail1Interface extends MialInterface
{
    /**
     * Send email from contact form
     *
     * @param string $replyTo Reply-to email address
     * @param array $variables Email template variables
     * @return void
     * @since 100.2.0
     */
    public function send($recipient, $replyTo, array $variables);
}

/var/www/html/magento/app/code/Amy/Contactform/Controller/Index/Post.php

<?php
/**
 *
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Amy\Contactform\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\Post
{
    /**
     * @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, $mail, $dataPersistor);
        $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. Your inquiry was submitted and will be responded to you as soon as possible.')
            );
            $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['subject'],
            $post['email'],
            ['data' => new DataObject($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($request->getParam('lastname')) === '') {
            throw new LocalizedException(__('LastName is missing'));
        }
        if (trim($request->getParam('address1')) === '') {
            throw new LocalizedException(__('Address1 is missing'));
        }
        if (trim($request->getParam('address2')) === '') {
            throw new LocalizedException(__('Address2 is missing'));
        }
        if (trim($request->getParam('city')) === '') {
            throw new LocalizedException(__('City is missing'));
        }
        if (trim($request->getParam('stateprovince')) === '') {
            throw new LocalizedException(__('State is missing'));
        }
        if (trim($request->getParam('zipcode')) === '') {
            throw new LocalizedException(__('Zipcode is missing'));
        }
        if (trim($request->getParam('subject')) === '') {
            throw new LocalizedException(__('Subject is missing'));
        }
        if (trim($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();
    }
}

/var/www/html/magento/app/code/Amy/Contactform/etc/di.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
     <preference for="Magento\Contact\Block\ContactForm" type="Amy\Contactform\Block\ContactForm" />
    <preference for="Magento\Contact\Controller\Index\Post" type="Amy\Contactform\Controller\Index\Post" />
    <preference for="Magento\Contact\Model\Mail" type="Amy\Contactform\Model\Mail" />
</config>

Answer 1

After struggling for days, I got the solution This is how you will be able to override the contact Model Mail.php file, I posted this answer, because it may be useful to others.

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

use Magento\Framework\Mail\Template\TransportBuilder;
use Magento\Framework\Translate\Inline\StateInterface;
use Magento\Store\Model\StoreManagerInterface;
use Magento\Framework\App\ObjectManager;
use Magento\Framework\App\Area;
use Magento\Contact\Model\ConfigInterface;

class Mail extends \Magento\Contact\Model\Mail implements \Magento\Contact\Model\MailInterface
{
    /**
     * @var ConfigInterface
     */
    private $contactsConfig;

    /**
     * @var TransportBuilder
     */
    private $transportBuilder;

    /**
     * @var StateInterface
     */
    private $inlineTranslation;

    /**
     * @var StoreManagerInterface
     */
    private $storeManager;

    /**
     * Initialize dependencies.
     *
     * @param ConfigInterface $contactsConfig
     * @param TransportBuilder $transportBuilder
     * @param StateInterface $inlineTranslation
     * @param StoreManagerInterface|null $storeManager
     */
    public function __construct(
        ConfigInterface $contactsConfig,
        TransportBuilder $transportBuilder,
        StateInterface $inlineTranslation,
        StoreManagerInterface $storeManager = null
    ) {
        $this->contactsConfig = $contactsConfig;
        $this->transportBuilder = $transportBuilder;
        $this->inlineTranslation = $inlineTranslation;
        $this->storeManager = $storeManager ?: ObjectManager::getInstance()->get(StoreManagerInterface::class);
    }

    /**
     * Send email from contact form
     *
     * @param string $replyTo
     * @param array $variables
     * @return void
     */
    public function send($recipient, $replyTo, array $variables)
{
    /** @see \Magento\Contact\Controller\Index\Post::validatedParams() */
    $replyToName = !empty($variables['data']['name']) ? $variables['data']['name'] : null;
    if ($recipient == 'General feedback'){
        $emails = ['aaa@gmail.com'];  // add your email list
    }else if ($recipient == 'Warranty'){
        $emails = ['bbb@gmail.com'];  // add your email list 
    }

    $this->inlineTranslation->suspend();
    try {
        $transport = $this->transportBuilder
            ->setTemplateIdentifier($this->contactsConfig->emailTemplate())
            ->setTemplateOptions(
                [
                    'area' => Area::AREA_FRONTEND,
                    'store' => $this->storeManager->getStore()->getId()
                ]
            )
            ->setTemplateVars($variables)
            ->setFrom($this->contactsConfig->emailSender())
            ->addTo($emails)
            ->setReplyTo($replyTo, $replyToName)
            ->getTransport();

        $transport->sendMessage();
    } finally {
        $this->inlineTranslation->resume();
    }
}
}

Answer 2

Have you tried the preference as below :

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Contact\Model\Mail" type="VendorName\ModuleName\Model\Mail" />
</config>

Answer 3

Mailinterface.php model is an interface class and we can't directly override magento's core interfaces. You can override Mail.php using preference like :

<preference for="Magento\Contact\Model\Mail" type="Namespace\Modulename\Model\MailOverride"/>

Thanks