How should this work, exactly? SMTP settings are in app.yml, and they need to stay there because they are meant to be configured during set up, before the first administrator account is created. I don’t think that it’s reasonable for Discourse to find and update its own app.yml file, so what alternatives are there?
The only reasonable way to do this that I see would be a site sitting for “ignore the SMTP configuration in the container definition and use these settings instead”, which sounds like a support nightmare to me (since now there are two places where the mail configuration could be messed up).