Mail is one of the hardest services to manage. Actually, mail is pretty simple in and of itself: there’s protocols people use to access their mail (such as IMAP and POP), protocols used to communicate between mail servers and send mail (SMTP, SMTPS) and then there’s a database of mail and user information. In macOS Server 5.4 for High Sierra, all of these are represented by a single ON button, so it really couldn’t be easier, once you can just enter email addresses into the Users section. But then there’s the ecoysystem and the evil spammers. They’re totally the worst. Like ever. As the former systems administrator of a large number…