I’d definitely take a look at the guide that @hansen referenced. It’s a good starting point and will get you moving in the right direction.
When it comes to e-mail, setting up Postfix or Sendmail alone will not “just work” as expected, if your intent is to stay out of SPAM/Junk folders.
SPF, DKIM, DMARC, and PTR (Reverse DNS) are the main things you need to look at and setup if you want to stay out of SPAM/Junk folders. Without these, the vast majority of what you send will land in these folders, unless the e-mail address is whitelisted for every single recipient you send to.
That being said, managing a mail server can be a major pain. I’ve done it, I’ll most likely end up doing it again in the future, but I don’t like it. There’s simply so/too many factors and because of this, that’s why so many third-party solutions, such as SendGrid and Mailgun, have popped on to the scene.
If you’re wanting something simple, less complex, etc – running your own mail server won’t provide that. I’d recommend looking at SendGrid, MailGun, Google Apps (G Suite), etc. Many are free for a certain number of monthly mails, others are paid (specifically G Suite).