I didn't mean email alias files. The article explains what it means by "email aliases", and it's something different.
I meant the files that contain aliases which are used to configure MTAs, which thus create email aliases.
Still not what either I or the article is talking about. Yes, the person designing the service has to know about alias files (or whatever other back end is being used), but the user doesn't have to know or care. I'm talking about what the user sees.
I actually use the database to store all the different aliases, then Postfix does a database lookup to see if they exist or not.