Airflow don’t send emails of dags on failure

I have Airflow running inside docker, we already configured the SMTP in the airflow.cfg and created a test dag with email on failure enable, but it fails with the error "WARNING – section/key [smtp/smtp_user] not found in config"
As SMTP we use mailgun through port 587.
Do you know if there is another configuration file that needs to be edited?

Here it is the log, airflow.cfg, and the DAGs settings.

Dag log error

Airflow.cfg

Test Dag

Something that I’ve noticed is that when it fails, it points to configuration.py (line 13) instead of airflow.cfg, during the docker build process we already change this to use airflow.cfg.
If we go to the admin tab to the configuration settings it is pointing to /usr/local/airflow/airflow.cfg.

Thanks, best regards.

Source: Docker Questions