Beyond email open tracking

by | Sat 6 Jun, 20

Email metrics are an important part of an email marketers work. Making sure the content you are producing, the emails you are sending and many other factors are doing as well as possible to get your subscribers to take the actions you want – either sales, registering for an event or downloading your latest whitepaper.

One metric that is constantly mentioned is email open rates. In this blog post we are going to discover the facts around open rates, how to use them and combine them with other metrics and how you can look beyond them to constantly improve your email marketing.
Email open tracking

In order to track email opens, email service providers (ESPs), such as mailchimp, include a piece of code in every email sent to subscribers. Most commonly this short string of code houses a 1×1 pixel image, the rest of the HTML surrounding it is there to hide it from your emails appearance – No one wants a 1 pixel white dot ruining their all black background!

Mailchimp tracking pixel
<img src=”″ height=”1″ width=”1″>

Marketing emails created with HTML and sent using an ESP will use these images as a way to track if a user has opened an email. HTML is all loaded when a user clicks and opens the email, bringing it into view in their inbox – an email loads from top to bottom and when an image is requested from the server it is hosted on, your ESP receives some information, like the time it was downloaded and by including a unique string in the image address, who downloaded it.

Every tracking pixel will have a unique identifier – in the example above, the long string of letters and numbers after contain information that to mailchimp shows which email it was, who sent it and who it was sent to.

Email tracking pixel limitations
As we mentioned above, email opens are tracked using an image. If the person subscribing to your emails has images blocked, either by their inbox, corporate firewall, if they have a slow internet connection and images don’t load in time or they have chosen to not see images in your emails, there is no way to track if the email was opened using this technique.

Email clients that block images by default:
Windows 10 Mail
iOS Mail
Yahoo Mail app

Another limitation is that Gmail has a limit on the file size an email can be, this is measured at around 100kb – any HTML after this is not loaded and is cut off (see image below).

Beyond email open tracking

Most ESPs including mailchimp include the tracking pixel at the very end of the HTML email file, and in this instance would also not show your email as being opened.

TOP TIP: If you are sending a large email and the open rate is much lower than normal – check if your email was clipped in Gmail, by sending it to yourself (signing up for a gmail address is free!). Then check how many of your subscribers email address ends with or – although users can set up any address to be opened in gmail, this will give you a rough estimate.

Another limitation is some email clients actively blocking tracking pixels – such as the new platform – it’s sole mission is to keep email as private as possible and to stop email tracking, there are other services out there that do this as well.

So why use tracking pixels?
You may be wondering after all those limitations, why is something that can be unreliable given such a huge value in email metrics? The answer is – it’s the only way email marketers can track an email being opened with no other data.

Sometimes referred to as a vanity metric it should only give a small part of the overall picture in your email marketing. By combining the tracking pixel data with link tracking, goal tracking, conversions as a result of email specific links or deals and email replies – you can build up a good amount of email related data.

Tracking pixels
Don’t discount the data from tracking pixels completely, as mentioned above combining it with other metrics can give more accurate information, but it can also be used as a basis for comparing how some of your email components are working. Testing subject lines against one another, testing preview text, sender name, sender logos in A/B tests, which you can set up easily in Mailchimp – open rates from tracking pixels give a good starting point to work from.
Understanding Open Rate data

Beyond email open tracking

Within Mailchimp reports you have data on successful deliveries, total opens, last opened and clicks per unique opens.

Unique opens are the first time a subscriber opens your email – Total unique opens will give you the data on the number of times your email was opened, this shown as a percentage will be:

Unique opens
——————— x 100 = Open rate %
No emails sent


240 Unique opens
————————– 0.08 x 100 = 8% Open rate
3000 emails sent

Total opens adds up every time someone opens your email, for example if a user opened your email multiple times.

Last opened will be the last time a tracking pixel was downloaded and opened in a recipients inbox.

Clicks per unique opens combines unique open data with information on when a user clicks any link in your email, giving you the Click To Unique Open Ratio.

Other ways to track email performance

Looking beyond just open rate information from tracking pixels, a lot of other data could be used to gather data on email subscribers.

This data can be utilised in many different ways. One way is to use your ESP to track links, every ESP has the ability to add a unique identifier to every link in your email to see who clicked on it, when and how many times.

Website data could be combined with your ESP link tracking, by combining some strings in links that mean something to your website’s analytics, such as UTM parameters that Google analytics uses to see where clicks came from.

Clicks can also be another form of tracking email opens, if a user has clicked a link, they must have opened the email, but they may be blocking images or the tracking pixel has not loaded due to other reasons.

Using something unique to email, such as a promotional code, specific landing page or link, that leads to someone buying a product, signing up or downloading your content will be directly linked to your email.

For example: If you only shared a 20% discount code in one email, such as EMAIL20, you could attribute any sale that used EMAIL20 directly to that one email.

Similar to conversions, you could set up a goal for your email, this may involve something other than completing an action like a sale or download. For example, your goal could be to get users to click on more than one link in your email, read all the way to the bottom or visit more than one web page when they use your website.

Email actions
Actions users perform in emails, such as forwards and replies can also be used to measure email effectiveness. Mailchimp has the ability to track if an email has been forwarded on to another recipient and you can monitor your email replies to see who is communicating with you.

Although not a metric you want to increase, it is a useful metric to test your content. It is normal for users to unsubscribe when they are not interested in your emails, they may have no need for your content any more or change interests. But you want to ensure that this doesn’t increase a lot when testing new content.

With the rise in user privacy, tracking controls and the limitations on image tracking pixels it is important for email marketers to look at other ways to evaluate email performance. Combining the email metrics above as well as unique deals for subscribers and on site goals or tracking, email marketers don’t have to rely on email open tracking.

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