I ran mail servers for close to two decades. When I started, I started by porting Sendmail, UUCP, and listproc to Linux. For almost two years I’ve been considering running my own mail server again; I even have access to a Discourse forum that generates lots of mail (that I’m paying Mailgun to deliver) that I could use to warm up an IP, and it wouldn’t be the end of the world if some of that mail got classified as spam while things were getting started. I have a server that’s on an IP block that is not likely to be on lots of blacklist.
Those a near-perfect conditions for setting up a mail server. I haven’t done it.
If you’re sending fewer than 10K messages per month and have access to a credit card there is almost no reason to run your own mail server.
Another “easy” way to do it appears to be Mail in a Box. You can get help on getting it working from https://discourse.mailinabox.email/