@Kowlin Eh, the way I see it, email and other assorted protocols were developed back when there were no other protocols or similar services to build off of, so it was really just the wild west.
Also, it seems everybody trusted one another and nobody expected spam to even exist, so it was never conditioned for, so now we have all of these bolt-on things you have to do to make sure your mail isn't sent straight to the spam bin... SPF records, DKIM signing, etc...
It's a miracle email actually still works the way it does.
Yes, indeed, if you're looking to scale up to handle high concurrent user loads, scaling out horizontally is your best bet. We've got a client right now serving 700+ connections at the moment, and they're on four separate NodeBB instances. It's probably too much for what they need, but it's always nice to have more capacity than needed in case of spikes, etc.