Help me with setting up this image

Guys i am using this image for magento development. Everything works great, except i can’t make emailing feature work(magento does not send order confirmation or any emails other emails)

I never done any emailing related settings, everything was always handled by the host. Could you please explain how to set it up?

The image uses Sendmail. The instruction says " If sendmail has been enabled, make sure the container has a hostname assigned using the hostname field in docker-compose.yml or --hostname parameter for docker run"

But what should i put as hostname? What ports. Could provide sample set up function?