HandlerAbstract.php

<?php

namespace GoSale\RabbitMQ;

abstract class HandlerAbstract implements HandlerInterface
{
    /**
     * @var array
     */
    protected $payload;

    public function __construct($payload)
    {
        $this->payload = $payload;
    }
}

HandlerInterface.php

<?php

namespace GoSale\RabbitMQ;

interface HandlerInterface
{
    public function handle();
}

WelcomeClientMail.php

<?php

namespace App;

use GoSale\RabbitMQ\HandlerAbstract;
use Swift_Mailer;
use Swift_Message;
use Swift_SmtpTransport;

final class WelcomeClientMail extends HandlerAbstract
{
    public function handle()
    {
        // Create the Transport
        $transport = new Swift_SmtpTransport(
            getenv('MAILER_SMTP_HOST'),
            getenv('MAILER_SMTP_PORT'),
            getenv('MAILER_SMTP_ENCRYPT') ?? null
        );

        $transport->setStreamOptions([
            'ssl' => [
                'allow_self_signed' => true,
                'verify_peer' => false,
                'verify_peer_name' => false,
            ]
        ]);

        $transport->setUsername(getenv('MAILER_SMTP_USERNAME'));
        $transport->setPassword(getenv('MAILER_SMTP_PASSWORD'));

        // Create the Mailer using your created Transport
        $mailer = new Swift_Mailer($transport);

        // Create a message
        $message = (new Swift_Message('Welcome to the Go! Sale'))
            ->setFrom([getenv('MAILER_SMTP_USERNAME') => 'Go! Sale'])
            ->setTo([$this->payload->email => $this->payload->name])
            ->setBody("Hello {$this->payload->name}. Welcome to the Go! Sale.");

        // Send the message
        $result = $mailer->send($message);

        print_r($this->payload);
        var_dump($result);
    }
}