I set up my own mail server about a year before reading this book so the timing wasn't great, but still this was a good read. And fortunately I had chosen almost exactly the same software stack.
I will probably use this to go back through and fine tune a few things on my server...eventually. The rspamd config comes to mind. I don't think it is updating any definitions as I mark new messages as Junk.
This book was great for putting me to sleep. But that's OK! It probably isn't great to read something that amps you up and keeps you up.