Consider to use Mailpit since Mailhog isn't being maintained anymore.

Maybe we should consider using [Mailpit](https://mailpit.axllent.org/) instead, since Mailhog isn't being maintained anymore.

We can get inspired from [this config](https://github.com/vintasoftware/vinta-schedule-api/blob/d59db50da85f610029816c8d18a4fe6939df0856/docker-compose.yml#L56)