DSN Feature for SwiftMailer

!dsn_handler_for_swiftmailer.php

<?php
$mailer = Swift_Mailer::newInstance(
  Swift_SmtpTransport::newInstance('smtp.example.org', 25)
);

// NOTIFY=NEVER
$mailer->registerPlugin(new DsnPlugin([new NotifyHandler('never')]));

// --- OR ---

// NOTIFY=SUCCESS,FAILURE
$mailer->registerPlugin(new DsnPlugin([new NotifyHandler('success,failure')]));

DsnHandlerInterface.php

<?php
/**
 * Interface DsnHandlerInterface
 */
interface DsnHandlerInterface
{
}

DsnPlugin.php

<?php
/**
 * Class DsnPlugin.
 */
class DsnPlugin implements Swift_Events_TransportChangeListener
{
    /**
     * @var DsnHandlerInterface[]
     */
    private $_dsnHandlers;

    /**
     * DsnPlugin constructor.
     *
     * @param DsnHandlerInterface[] $dsnHandlers
     */
    public function __construct(array $dsnHandlers = [])
    {
        $this->_dsnHandlers = $dsnHandlers;
    }

    /**
     * Invoked just before a Transport is started.
     *
     * @param Swift_Events_TransportChangeEvent $evt
     */
    public function beforeTransportStarted(Swift_Events_TransportChangeEvent $evt)
    {
        $transport = $evt->getTransport();
        if ($this->_dsnHandlers && $transport instanceof Swift_Transport_EsmtpTransport) {
            $handlers = $transport->getExtensionHandlers();
            $handlers = array_merge($handlers, $this->_dsnHandlers);
            $transport->setExtensionHandlers($handlers);
        }
    }

    /**
     * Invoked immediately after the Transport is started.
     *
     * @param Swift_Events_TransportChangeEvent $evt
     */
    public function transportStarted(Swift_Events_TransportChangeEvent $evt)
    {
        //NOOP
    }

    /**
     * Invoked just before a Transport is stopped.
     *
     * @param Swift_Events_TransportChangeEvent $evt
     */
    public function beforeTransportStopped(Swift_Events_TransportChangeEvent $evt)
    {
        //NOOP
    }

    /**
     * Invoked immediately after the Transport is stopped.
     *
     * @param Swift_Events_TransportChangeEvent $evt
     */
    public function transportStopped(Swift_Events_TransportChangeEvent $evt)
    {
        //NOOP
    }
}

NotifyHandler.php

<?php
/**
 * Class NotifyHandler.
 */
class NotifyHandler implements Swift_Transport_EsmtpHandler, DsnHandlerInterface
{
    /**
     * @var bool
     */
    private $_hasDsn = false;

    /**
     * @var string
     */
    private $_notify;

    /**
     * NotifyHandler constructor.
     *
     * @param $notify
     */
    public function __construct($notify)
    {
        $this->_notify = strtoupper($notify);
    }

    /**
     * Get the name of the ESMTP extension this handles.
     *
     * @return bool
     */
    public function getHandledKeyword()
    {
        return 'DSN';
    }

    /**
     * Set the parameters which the EHLO greeting indicated.
     *
     * @param string[] $parameters
     */
    public function setKeywordParams(array $parameters)
    {
        $this->_hasDsn = true;
    }

    /**
     * Runs immediately after a EHLO has been issued.
     *
     * @param Swift_Transport_SmtpAgent $agent to read/write
     */
    public function afterEhlo(Swift_Transport_SmtpAgent $agent)
    {
        //NOOP
    }

    /**
     * Get params which are appended to MAIL FROM:<>.
     *
     * @return string[]
     */
    public function getMailParams()
    {
        return [];
    }

    /**
     * Get params which are appended to RCPT TO:<>.
     *
     * @return string[]
     */
    public function getRcptParams()
    {
        return $this->_hasDsn && $this->_notify ? ['NOTIFY='.$this->_notify] : [];
    }

    /**
     * Runs when a command is due to be sent.
     *
     * @param Swift_Transport_SmtpAgent $agent            to read/write
     * @param string                    $command          to send
     * @param int[]                     $codes            expected in response
     * @param string[]                  $failedRecipients to collect failures
     * @param bool                      $stop             to be set true  by-reference if the command is now sent
     */
    public function onCommand(
        Swift_Transport_SmtpAgent $agent,
        $command,
        $codes = [],
        &$failedRecipients = null,
        &$stop = false
    ) {
        //NOOP
    }

    /**
     * Returns +1, -1 or 0 according to the rules for usort().
     *
     * This method is called to ensure extensions can be execute in an appropriate order.
     *
     * @param string $esmtpKeyword to compare with
     *
     * @return int
     */
    public function getPriorityOver($esmtpKeyword)
    {
        return 0;
    }

    /**
     * Returns an array of method names which are exposed to the Esmtp class.
     *
     * @return string[]
     */
    public function exposeMixinMethods()
    {
        return [];
    }

    /**
     * Tells this handler to clear any buffers and reset its state.
     */
    public function resetState()
    {
        //NOOP
    }
}

Is it possible to set ORCPT parameter?
RCPT TO:<user@example.com> NOTIFY=SUCCESS,FAILURE ORCPT=rfc822;user@example.com