Are open rates a good measure of campaign success?

The answer might surprise you once you understand how open rates are calculated and the technical complexities affecting those calculations. If you're ready for a two-minute primer on open rates, grab a cup of chamomile tea and read on.

In this article, I cover these topics:

On the surface, the answer is simple. Somebody goes to their inbox and opens a message. That action counts as one open event.

To calculate the open rate, take the total number of open events divided by the total number of delivered messages. Voila! If your open rate is somewhere between 20 and 28%, your campaign's performance is, well ... average.

Here's where the math gets messy.

Tracking an open event depends on an invisible image added to every message (an industry standard, BTW). The image is tiny (just one pixel), so nobody can see it, and it has no effect on your message design.

Whenever somebody opens an email message, our server gets a call to load the email content into the recipient's email client. That call includes the tracking pixel. Every tracking pixel in every message has a unique URL. That means we can track who opens the message and count the number of open events.

With this new information, let's change our math calculation a bit. An open rate is the number of tracking pixel calls divided by the total number of delivered messages.

Still with me?

The tinyAlbert campaign dashboard shows unique opens. This figure counts the number of first open events and ignores multiple opens. That's different from Total Opens, which takes all opens divided by total delivered messages, including, for instance, the same message opened multiple times by one recipient.

Nope. Multiple factors can overstate or understate open rates. Here's why.

Some email clients (e.g. Gmail and Apple Mail) pre-load email images, including the tracking pixel. That means the email message sends a call to the server even though the recipient did not open the message. Why is that important? Pre-loading can inflate open rates.

Some email clients block images from loading, which includes the tracking pixel. If blocked, the message won't send a call for the tracking pixel. That means a message opened by a subscriber won't register as open. Privacy features in Apple's iOS 15 (and beyond) prevent email tracking. The result is underreported open rates.

Every email you send in a campaign has two versions: HTML and text-only. The text-only version has limited formatting and looks like it was created with a typewriter. Almost every email client reads the HTML version, and few people choose the text-only version if that option is even available. Even still, it's worth noting that text-only messages remove the tracking pixel (along with all images).

That means the only way to track reader engagement (with text-only messages) is by tracking the number of links clicked in the message, which I discuss below.

A Greek philosopher once opined that change is the only constant in life. That's an accurate description of email marketing.

Technological change has made open rates less accurate. Once the yardstick of email marketing performance, it's now a legacy measure that has some value, though it may be diluted.

Email marketers look at a basket of indicators when they want a global understanding of campaign performance. The basket includes include bounce rate, delivery rate, and unsubscribe rate.

I'd argue we should keep open rates in the basket, though more attention should shift to click rates if we want an accurate measurement of reader engagement.