Can’t send emails due to failed internal dns resolution

Ok, thanks a lot, it all finally worked,
so:

I’ve changed the DOCKER_OPTS:
DOCKER_OPTS="--ip 127.0.0.1"

then rebuild the app with the quotations:
DISCOURSE_SMTP_AUTHENTICATION: 'none'
DISCOURSE_SMTP_ENABLE_START_TLS: "true"

Thx a lot!