Email Marketing Metrics: Open Rates


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 Many of our webinar attendees and customers are unclear how email open rates are tracked, and email open tracking has some caveats so it is important to understand the tracking mechanisms. 

In this 3-part blog we’ll cover email marketing metrics – starting with email open rates.  Other important email marketing metrics you may want to review include email delivery rate and  email click-through rates.

First, a few quick definitions:

  • Total Opens – Total email opens measures the total number of times your email campaign has been opened. For example if you send a campaign to 10 people and 4 people each open the email twice, a total of 8 opens will be reported (most email providers report this number). 
  • Unique Opens – Unique email opens measures the total number of unique recipients who opened your email.  If 4 people each open your email twice, the unique email open rate will be 4.

Both metrics are important.  Unique opens measures the number of people who are ‘engaged’ with your content – the portion of your email audience that is reading your emails.  Total opens are also important – if the ratio of total opens to unique opens is high (ie on average, people are opening your email multiple times), this indicates people may be passing along your email to colleagues and/or they may be saving your email for reference and referring back to it.

How Email Opens are Tracked

When an email is sent to a subscriber, email providers embed a transparent, 1×1 pixel gif image in the email.  When the subscriber opens your email, all images, including the tracking pixel, are fetched and we are able to detect the exact time the recipient opened the email.  However if images are not fetched (that is – if your recipient has disabled image display), the email open cannot be tracked. 

Here’s an example of an email that has been opened in the inbox, but will not be counted as having been opened:

Email images blocked


In the following email, images are being displayed, so we are able to detect the email has been opened:

 Email images not blocked

The two emails are identical, but the top email will be reported as ‘unopened’ even though we’re reading it. 

Problems with Email Open Tracking

As you can see, tracking email open rates isn’t entirely accurate – though it’s still an important email marketing metric.

Images Disabled by Default

For security reasons, more than 70% of email clients are set to block / not display images by default. Your recipient has to either explicitly display images for all emails (or at least for emails sent from you), or select ‘display images’ on each email.  Once image display is enabled, the email

Inbox Preview Mode

Most email clients (Yahoo and MS Outlook for example) have an inbox preview pane.  If image display is enabled and the recipient scrolls through their inbox and your email is displayed in the preview pane and images are fetched – then the email will be marked as an open even though the recipient didn’t necessarily read the email.  There isn’t a simple way to determine if the recipient just flipped past the email in their inbox or whether they kept the window open for several minutes and read it.

Text-Only Emails

Open rates can’t be tracked for text-only emails.  The best that can be done here is to calculate click-through rates.  Of course anyone who clicks a link had to open the email so it is possible to track a subset of the recipients who open your text-only campaign.

Why Email Open Rates are Still Useful

Although open rates are not as accurate as they once may have been, email open rate metric is still useful for comparing your relative results vs. other campaigns you send.  And since all email providers (ESPs) are forced to sue the same mechanism to track open rates, comparing your open rates between one ESP and another is generally a valid comparison.

How to Improve Email Open Rate Accuracy

You can improve the accuracy of email open rate reporting. Give your recipients a reason to turn images on for your emails. Here are 2 tips:

Add this ALTernate text to an image “Please turn on images for the best newsletter experience. “ or “Please select ‘Always Display Images from’ 

If your subscribers trust you (and they should – if you’re sending relevant information at the right frequency), encourage them to whitelist you by adding your email address to their address book, or by selecting ‘Always Display Images from




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