I recently set up smtpd for futurist.city following this tutorial, and it was super easy! In fact, it was so much easier than I thought. Email has always been a daunting task in my mind, and I was afraid it would always be that way. But, sure enough, I got it set up in around an hour. Except wait, I can't send emails externally? But I can receive external emails? This is weird. Okay, maybe there's something else going on. As with most of what I've learned about OpenBSD recently, I headed to the IRC chat. I figure out that the VPS host blocks the SMTP port by default, and you have to fill out a form to get it unblocked. I do so, and shortly after the port is unblocked. I'm excited, so I try to send another email and it sends, but I can't see it? Okay, apparently iCloud is refusing the connection. Gmail actually does receive it, except it sends it straight to spam? Okay, I'll enable all of the spam protection, and use SPF and DKIM. I try again. Same result. Weird... I go to the IRC chat again: "oh yeah that's just how email is, don't take it personally"
By the way, if you're a futurist resident, you can send/receive emails now (sort of... spam filters aren't allowing it yet)! Send me an email: email@example.com, and read the manual for more.