I want to develop.
I was confused trying to set up SMTP so I could create (and then email confirm) a new user. The docs talk about app.yml which comes from standalone.yml. These files are not in the developer install. So I grabbed them from the docker install and things went downhill from there.
What I needed instead was to run
bundle exec sidekiq >& /dev/null &
mailcatcher --http-ip=0.0.0.0
Then in a browser, go to http://localhost:4080. Sent emails will be received by mailcatcher and shown in its web ui. When you catch the email with confirmation link change localhost:3000 … to localhost:4000 … and paste that into the browser. It was as simple and intuitive as that 