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How Reliable Are Your Email “Open” Stats?

Ever wonder how open rates are calculated for your marketing emails? Here’s a glimpse at how they work, and a caveat about how reliable your open rate numbers are:

How Opens Are Counted

When you compose an email and send it through ClickDimensions, our system inserts a tiny, transparent, 1×1 pixel GIF image into the email. This GIF is hosted on our system. When we insert the GIF into an email, we also insert a unique identifier at the end of its address. That unique identifier corresponds to the recipient to whom you’ve sent the email.


So, for example, if the GIF is hosted at http://files.mycompany.com/tracking.gif, we’ll add a unique id for each and every email recipient to the end of the address in the email’s HTML. Now the URL for the tracking GIF might look like this: http://files.mycompany.com/tracking.gif?_id=1234567890. (This is simplifying things a bit – the image is actually generated programmatically – but you get the idea!)

Now, when the recipient views the email you’ve sent, our web server sees the request for that transparent GIF and the attached id, and now it knows who viewed the email.

When ClickDimensions sees that Joe opened an email, we record an “Open” email event in your CRM. Now you can see that Joe opened the email you sent.

Simple, right?

Tracking GIFs are a proven and widespread method for tracking whether someone opened an email. They are used by most every email provider out there. So what could go wrong?

  1. Most email applications today block the display of images by default. This is true of desktop email applications like Outlook, as well as webmail providers like GMail and Hotmail. As shown in the illustration below, a recipient can actually open and read your email without it being possible to count the “Open” event.
    The recipient would need to click Outlook’s informational message to download all the pictures for the email, including your tracking GIF. In some email applications, if the user adds the sender to the “Safe Sender” list or whitelist, then images will always be displayed automatically in emails from that sender.
  2. An Email Can Be Forwarded. So what would happen if I received the email above, didn’t tell Outlook to download all the pictures, and forwarded it to my mom (who is still using Outlook 2000 on Windows ME)? Well, in that case, the tracking GIF would be downloaded because her outdated system doesn’t block tracking images automatically, and the pictures would be displayed for my mom. But the unique ID that was appended to the tracking image is still correlated to me. So our system would think that I opened that email.
  3. Some people don’t clean out their inboxes. Another potential wrench in the cogs of your attempts to measure your readership’s engagement is that there are some people (we won’t name names!) who don’t have great inbox management habits. You send them an email and it stays in their inbox for months. Years even. Each time they happen to scroll past it and the email is displayed in the preview pane, the tracking GIF is loaded, and an Open event is counted.

So What’s The Takeaway Here?

The potential for missing real “opens” or counting opens that shouldn’t count is why we focus on “Unique Opens” – how many people opened your email (or, in other words, downloaded the tracking GIF) as opposed to how many times your email was opened – to calculate your open rate.

In this example, there were 6,470 total messages sent, and 1,953 unique opens – a 30% open rate:

Since we know that the Open rate may not be 100% accurate – it’s likely quite a bit higher than the total number of unique opens that were possible to record – then what good is it? Well, the trend is your friend! Looking at your unique open rates over time can give you an idea if you are getting better or worse at reaching your audience with relevant messaging. (Check out this blog from a few months ago to get some cool charts to monitor your email statistics trends!)

Happy Marketing!

About the Author:

Matt Wittemann is a 13-time Microsoft Dynamics CRM MVP and ClickDimensions' Senior Director, Pre-Sales Consulting.

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