Honestly, I've being building and running ISPs of every scale since the late '80s, and I'm a source code contributor to some widely used mail servers, so I am t

Honestly, I've being building and running ISPs of every scale since the late '80s, and I'm a source code contributor to some widely used mail servers, so I am that very model of someone who others might suppose knows what they are doing, and still the prospect of setting up a reliable email service from scratch today would give me pause to say "are you sure an existing service can't be used"?