Seven myths and two truths about email
My favorite:

[myth] Engagement is the new reputation. Actually, reputation metrics have always been about engagement, which is what complaint data and sender reputation reflect.

Yes. This.
Reputation, permission, all of those things are a way to quantify one simple fact: Do recipients want this mail from this sender?
Send mail people want and generally it will get into the inbox. Send stuff they don’t want (or don’t care if it shows up or not) and suffer delivery problems.

engagement • Reputation