Setting up a kbin instance. Need help with .env file.

I'm experimenting with setting up a kbin instance but struggling with understanding what's up and down in the .env file. What additional services do I need to install? Do I need to setup and configure smtp for sending mails? Should I change the domain to my intended domain name, or do I have to wait until I have a reverse proxy etc. set up?

Anyone have any experiences to share or an example of a configuration?