What kind of KPIs would you track for email marketing if you weren't selling anything?

First - You are always selling something. It might not be immediate, you might not have a call to action in every email, or you might be building up to a sales pitch but you are always selling something. Even Quora's emails are selling something - engagement. If people are using Quora more, they get more page views, more visitors, more content, more answers, more active users - ultimately leading to higher valuation/ opportunity for advertising/ offers to buy the company/ etc. Figure out your end game. Why are you sending out your campaigns? What do you want to achieve? What is a satisfying outcome? Once you answer these question you will have your answer what KPIs to measure. Edit: Provide more information about your campaigns and maybe you will get more precise answers.