Yii2 Mail Debug to file

web.php

<?php

// config/web.php:186

        'mailer' => [
            'class' => 'yii\swiftmailer\Mailer',
            'messageClass' => 'app\components\Message',
            'htmlLayout' => '@app/modules/account/mail/layouts/html',
            'useFileTransport' => true, // <--
        ],