Task: Set up your own SMTP server (you're the only user). Use OpenBSD and its own SMTP server.

Expectations: Ok, this should be pretty simple. I guess I'll just need to open this configuration file, specify the path to my SSL/TLS certificate, and create an MX record in my DNS.

Reality: You need all of that plus 20 other steps to protect yourself against all the ways in which bad people may misuse your server or damage your identity. You don't want those things to happen, do you?