How Open Rate Really Works

There’s a lot of disagreement about what the thing called “open rate” actually measures and how it works. Obviously, at some basic level we all understand it purports to quantify the number of recipients who actually open our email. But what about text messages? How about the preview pane? What about a user who checks her email offline?

Well, I’m here to set the record straight and put these questions (and more) to bed — once and for all.

Method to the Madness: Counting Opens

Gauging the number of opens your email receives is achieved by embedding an image into your HTML message. The image isn’t actually distributed in the message, but is rather referenced from within the message, as with all HTML documents. Each time someone opens that email, he loads up the HTML document and renders it in his email client.

As the email is rendered, the recipient’s email program must request a copy of that image from your server and attempt to load it in the message. Count the number of times that image is requested and — voilà! — an open rate.

If you send a message to 10,000 recipients and log 5,000 requests for your embedded image, you can safely say you’ve got an (approximate) open rate of 50 percent. Strictly speaking, the open rate isn’t the actual number of people who opened the email but the number who requested the embedded image.

Preview Panes and Other Banes

Armed with that understanding of open rate’s basic mechanism, you should have no problem with the preview pane. If someone reads your message in her preview pane and the preview pane renders HTML (e.g., Microsoft Outlook 2000) — boom — she’ll request your embedded image and register an open.

If the reader moves down through his inbox and passes your message without actually reading it, does that record an open? No. If the message isn’t loaded in the preview pane, it won’t give you an open. Even if the user stops momentarily on the message, long enough so it starts to load in the preview pane, but he moves on before anything is requested from your server, you’ll get no open. Only if he stops long enough to load the entire message (and your embedded image) will an open be recorded.

Consider putting the embedded image you’re counting at the end of the message. That way, it’ll be the last thing rendered. It will count as an open only for people who’ve had the message open for a few seconds at least. I call that a “true open.”

Here’s a rundown of other banes:

Don’t Worry, Be Happy

With so many variables and unknowns, it’s tempting to throw up one’s hands and kiss open rate goodbye. Don’t do it! Yes, it’s true a small number of opens will be false or duplicates. Yes, it’s true there are a handful of cases where opens are underreported or fail to be reported at all. As long as you treat the number as a ballpark figure, not some unerringly precise scientific standard, you should be in good shape. Think of it as “(approximate) open rate.”

Remember: Probably the most important thing you can learn from open rate is how your behavior influences it. Most other variables (firewalls, dial-up, etc.) remain the same from mailing to mailing. What willchange is your subject line, your subscriber base, and all the things you can do to help increase your open rate. Watching the pluses and minuses weekly is where the action is. Growth is probably more important than baseline. (Approximate) open rate is just perfect for that.

Got a question? Think I’m full of it? Let me know — send me email!

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