Swiftmailer not logging anything

I am unable to see any logs from Swiftmailer. I have the following in my config file.

'log' => [
    'traceLevel' => YII_DEBUG ? 3 : 0,
    'targets' => [
            'class' => 'yii\log\FileTarget',
            'levels' => ['error', 'warning', 'info', 'trace'],
            'categories' => ['yii\swiftmailer\Logger::add'],

and I also have 'enableSwiftMailerLogging' => true in my mailer component.

However, when I check /frontend/runtime/, there are no logs even when there’s a clear error in the email transport.

What am I doing wrong here?

This is on a production environment btw.