Log all emails sent with Swiftmailer

LoggerPlugin.php

<?php

namespace App\Swiftmailer;

use Psr\Log\LoggerInterface;
use Swift_Events_SendEvent;
use Swift_Events_SendListener;

class LoggerPlugin implements Swift_Events_SendListener
{
    /**
     * @var LoggerInterface
     */
    protected $logger;

    /**
     * @var array
     */
    protected $alreadySend = [];

    /**
     * @param LoggerInterface $logger
     */
    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    /**
     * @param Swift_Events_SendEvent $evt
     */
    public function beforeSendPerformed(Swift_Events_SendEvent $evt)
    {
    }

    /**
     * @param Swift_Events_SendEvent $evt
     */
    public function sendPerformed(Swift_Events_SendEvent $evt)
    {
        $messageId = $evt->getMessage()->getId();

        $context = [
            'message_id' => $messageId,
            'subject' => $evt->getMessage()->getSubject(),
            'from' => $evt->getMessage()->getFrom(),
            'to' => $evt->getMessage()->getTo(),
        ];

        if ($evt->getTransport() instanceof \Swift_Transport_SpoolTransport) {
            $this->logger->info('An email has been added to spool', $context);
        } else {
            $this->logger->info('An email has been sent', $context);
        }

        $this->alreadySend[$messageId] = true;
    }
}