let me repeat something i wrote in another thread: bringing up the smtp daemon in basic configuration (and, by the way, my preferred one is exim) is trivial. managing working and usable mail service is not.

it's a process! you need to reserve time for that! you need to understand basic networking, you need to intimately know how dns works. you need to know how to use swaks. you need to know your RFCs, and the subtle breakages of the protocol that you need to introduce in order to reduce the amount of spam you're receiving. you need to understand why everything that SPF promises is a lie, but you'll be using it anyway. you need to know how DKIM works, and what is the true meaning of DMARC. you will learn that google wants you to use experimental features in order to be able to deliver your fucking mail to them. you need to understand that the anti-spam blacklists are managed by fucking racketeers, and that you can't avoid them. you need to understand the difference between sending mail and receiving it, and why a correctly configured MX record does absolutely nothing to improve the ability to deliver remote mail. you need to have time to deal with petty tyrants on a mission, and with oblivious bureaucracy of large providers, and learn to be happy if you can reach a human person on the other side at all.

and that's just the SMTP part.