Unique Opens vs Total Opens: What’s the Difference, and Why Does It Matter?

  • May 15, 2019

By Verity Jennings

Blue email icon
Share Article

Seeing a healthy, robust email open rate when tracking the performance of an email marketing campaign is a great feeling. For an email marketer, there’s no higher praise for email subject line prowess.   

And we should know. Here at Phrasee, we’ve tracked the open rate performance of millions of email subject lines across dozens of industries and thousands of campaigns. It’s a huge part of what we do. There’s something important we learned very early on in this process, something everyone tracking subject line performance and open rates should take note of…  

Not all opens are created equal. 

In the world of email open rates there are opens, and then there are “opens”. Knowing the difference can (and often does) mean the difference between gathering meaningful data that successfully optimizes email subject line performance and meaningless data that optimizes very little at all. Tracking the total opens an email campaign generates can be helpful, but tracking the unique opens is where the subject line optimization money is.   

Here’s why …    

What’s the difference between total opens and unique opens?

Total opens are calculated by tracking the total number of times an email is opened, regardless of how many individual subscribers those opens are generated by.  
– One email. One open. One “total open”.

Unique opens, on the other hand, are calculated by counting the first time a single subscriber opens an email. All subsequent opens from that subscriber are ignored.  
– One email. One recipient. One open. One unique open.

The difference is a subtle but important one. 

Why would a single subscriber open the same email multiple times?

As strange as it may sound, a single subscriber generating multiple opens of the same marketing email is actually quite common. There are a few reasons for this:  

  1. The subscriber forwards your email to someone else, who then opens it (this is a good thing!) 
  2. The subscriber opens your email, likes what they see, and returns to open the email again later to follow up (this is also a good thing!) 
  3. The email client counts an open every time the subscriber scrolls through their inbox
  4. Some sort of bot is associated with the email client, or is being used by the recipient’s domain (this can be part of a company’s IT security infrastructure). When this happens, a bot is used to click each link within the email, to alert companies to potential phishing scams.

Why does it matter?

When it comes to optimizing a brand’s email subject lines to maximize opens, performance data is crucial. It is simply the only tool we email marketers have to gain insights into what subject line language works on our audience and what subject line language doesn’t.   

While on the surface the arguments for counting multiple opens from the same recipientforwards and returning readers (some of which result in actual sales)might seem to outweigh the risk of those multiple opens coming from bots or agents, the truth is actually quite the opposite. The reason for this is simple: it’s a matter of scale.  

A few forwarded emails and a handful of returning readers here or there generally have a very small impact on the total number of opens a campaign will generate. When dealing with bots or agents, which are capable of opening an email a thousand times in a relatively short period, the impact on campaign performance metrics can be significant. 

OK, now what?

With bots at the helm, a small number of accounts can often be responsible for a disproportionate number of total opens. That would be great if they were also responsible for a disproportionate number of sales.  

Sadly, they aren’t.  That’s why the unique open rate is the most robust metric for measuring email subject line performance and quality. 


100 opens by the same person = 1 unique open

100 opens ≠ 100 different people opening your email

Stop measuring for total opens. Make the switch to unique opens and get ready to start optimizing your email subject lines to maximize the ROI-generating impact of all your future email marketing campaigns.