What is the absolute, bare minimum, no-hassle, hopefully idiot-proof way of setting up a local smtp server?

If you're going to say postfix, what are these alledgedly bare minimum, idiot proof steps to setting it up?

I'm sort of amazed at how difficult it seems to find this anywhere. I need:

• a locally hosted smtp server that sends mail to the internet.
• no tls or saslauth or whatever.
• only allows mail to come from localhost.
• no relays.

It seems like there should be some software package somewhere where you install, set up an account and then you have a local smtp server.

I'm not a sysadmin. People say postfix is dead simple but maybe I'm doing it wrong, all the setup docs I see are quite complicated, I actually don't have a spare hour to spend debugging a mailserver. I just want to send mail to the internet. Is it really that hard?