Access Symfony config parameter in service

// src/Service/MessageGenerator.php
namespace App\Service;

// ...

use Symfony\Component\DependencyInjection\ParameterBag\ContainerBagInterface;

class MessageGenerator
{
    public function __construct(
        private ContainerBagInterface $params,
    ) {
    }

    public function someMethod(): void
    {
        // get any container parameter from $this->params, which stores all of them
        $sender = $this->params->get('mailer_sender');
        // ...
    }
}