Magento 2- Send mail using your smtp server

Here we learn how to send mail  using our smtp detail in magento2

For this we need to override mageto \Magento\Framework\Mail\Transport class by your custom model class

We can do it in two step

1# For override we need to write code in module di.xml file at location app/code/NameSpace/ModuleName/etc

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <!-- for override magento default Transport class with our custom module model-->
    <preference for="\Magento\Framework\Mail\Transport" type="NameSpace\ModuleName\Model\Transport"/>
</config>

2# Now we’ll define our  Transport model in our custom module

<?php
/**
 * Mail Transport
 */
namespace NameSpace\ModuleName\Model;

class Transport extends \Zend_Mail_Transport_Smtp implements \Magento\Framework\Mail\TransportInterface
{
    /**
     * @var \Magento\Framework\Mail\MessageInterface
     */
    protected $_message;

    /**
     * @param MessageInterface $message
     * @param null $parameters
     * @throws \InvalidArgumentException
     */
    public function __construct(\Magento\Framework\Mail\MessageInterface $message)
    {
        if (!$message instanceof \Zend_Mail) {
            throw new \InvalidArgumentException('The message should be an instance of \Zend_Mail');
        }
         $smtpHost= 'xxx.xxxx.xxx';//your smtp host  ';
         $smtpConf = [
            'auth' => 'login',//auth type
            'tsl' => 'tsl', 
            'port' => '587',
            'username' => 'xxxx@xxxxx.xxx',//smtm user name
            'password' => 'xxxxxxxxxxxxxx'//smtppassword 
         ];

        parent::__construct($smtpHost, $smtpConf);
        $this->_message = $message;
    }

    /**
     * Send a mail using this transport
     * @return void
     * @throws \Magento\Framework\Exception\MailException
     */
    public function sendMessage()
    {
        try {
            parent::send($this->_message);
        } catch (\Exception $e) {
            throw new \Magento\Framework\Exception\MailException(new \Magento\Framework\Phrase($e->getMessage()), $e);
        }
    }
}

Now all mail goes from your magento 2 instance using your smtp server