Delivery and engagement

Tomorrow is the webinar Mythbusters: Deliverability vs. Engagement. This webinar brings together the ISP speakers from EEC15, plus Matt from Comcast, to expand on their comments. There’s been some confusion about the impact of engagement on delivery and whether or not senders should care about recipient engagement.
My opinion on the matter is well known: recipient engagement drives delivery to the inbox at some providers. I expect tomorrow we’ll hear a couple things from the ISPs.

1. ISPs do monitor engagement, even if they do it differently than senders thought.
2. Engagement is important for inbox delivery at some ISPs.
3. Different ISPs have different ways of making inbox decisions.
4. Engagement will matter more in the future.

But what is engagement? Engagement means recipients are interacting with emails. Senders measure engagement by watching users load images and click on links. ISPs measure engagement by looking at what users do with emails (file, reply to, save, open, delete without opening, spam). The engagement measures are different, and they give each group different data.
Measurements by the ISPs also apply to many factors inside the email. Most of the big ISPs have some mechanism to allow recipients to identify an email as spam. Some ISPs provide this information back to senders in the form of a feedback loop (FBL). FBLs are tied to IP addresses (or in some cases d= values in the DKIM signature) but complaints count against other parts of the email, too. Yahoo, for example, keeps track of complaints against specific URLs in a message and will block mail that contains a URL that gets too many complaints. I’m sure they’re not the only provider that tracks complaints and URLs.
Senders are much more limited in what they can track for engagement: image loads (opens) and clicks. These measurements have always been proxies for what the ISPs are measuring, but they’re what senders have to work with.