Sure. But if the "second-generation MTA" is next to impossible to learn how to configure, it doesn't really matter how good it is technically - it's unuseable u

Sure. But if the "second-generation MTA" is next to impossible to learn how to configure, it doesn't really matter how good it is technically - it's unuseable unless configuring mail servers is literally your job, or you're happy copy-pasting someone else's config. Perhaps, one day, the Postfix people will realise that, but they apparently don't now. I ran into a configuration issue with exim in the last few months that prevented me from receiving some email from Amazon SES. The logged error told me at what logical step in the process it happened, and contained a user-configured error message on that specific step, which allowed me to quickly find and update it. That's something I never got from Postfix. Postfix's configuration is a completely flat mapping on a fixed pipeline, where that pipeline is not properly exposed to the user, and the documentation is not well-ordered outside a handful of quick tutorials - postconf.5 lays out the options in alphabetical order, not according to what part of the pipeline the options affect.