I am installing Docker on a host where all applications are already containerised including the main smtp server.
When I try and relay mail from discourse to this smtp server it fails because the server cannot do a reverse lookup on the Discourse server IP. This works fine with my other containers because using docker compose I am allowing access to the mail server docker network using for example something like
services: php-apache: networks: - mail_server networks: mail_server: external: true
How can I achieve this with Discourse so that Discourse service container and the mail server service container can communicate with each other directly?