Nothing gated. Read all three, run the free check on your own domain, and only leave details if you want the written version.
Every record and term named above appears in the deliverability glossary. Three sequences taken apart, ending with what the fix is worth in money, are in the case studies, and longer pieces sit in the library.
Authentication, reputation and the boring records that decide whether anything you write is ever seen.
The wait between messages is a decision, not a delay. Event driven against calendar driven, and when to stop.
The machine ends where a person starts, and most sequences never build that ending.