What is an open?

I was having a discussion today with a few industry colleagues about engagement and open rates. It was a good discussion and inspired a couple blog posts. Engagement totally matters, Engagement affects deliverability, and ISPs should be the last of your concerns.
I think they’ve covered the engagement issue pretty well, but what I wanted to talk about was metrics, specifically opens. Open is a fairly simple word, and it’s used in email all the time. Recipients open email. Mailbox providers measure that open. Senders measure that open.
It’s critical to remember, though, that open rates as measured by free mailbox provider and open rates tracked by a sender are not really the same thing. They’re measured in very different ways, and there is not a 1:1 mapping between the two measurements.

• Free mailbox providers actually track that the message was opened. They can see the status change from “unread” to “read.”
• ESPs track when a recipient loads an image.

ESPs can’t track the status of a message inside the recipient’s mailbox. And free mailbox providers don’t need to track image loads.
So even though both groups claim they are tracking opens, how they’re tracking gives different data to the people measuring the information. Gmail sees me open mail all the time. Most of my clients never see me open an email in my gmail account.
Free mailbox providers and senders are using the exact same word (Open) to describe different things (rendering an image vs. actually opening the mail). I think these things are different enough to say that an open as measured by a free mailbox provider and an open measured by the sender are not the same at all.
The crux of it is that even though mailbox providers use the metric of “open” to look at engagement and even though senders use the metric of “open” to look at engagement, they’re actually looking at two totally different things.