Introduction To Marketing Technology Course

How to track Email Opens

Imagine you had something important to say to someone. And that only way you could say it was through an email.

It could be professing love.

Or applying for a job.

Or seeking an advice.

Or apologizing.

You took days to write this email, poured your heart and soul into it, mustered the courage and hit the SEND button.

Now begins the waiting. Agonizing waiting.

Did they open the email yet?

It has been a day and no reply. Did they open yet? Surely they must be busy!

Two days gone! Still no reply!

Three days gone! Still no reply! Did they open? Surely, they must have opened it! Did they not like what I wrote? They must think I am desperate! Or Stupid. Or Stupidly desperate! I should never have sent the email. Why did I send the email? What was I thinking!

Four days later – A reply arrives! Thank you for your thoughtful mail! I was on vacation! I just came back and saw it! Lets meet in person. Does tomorrow noon work?

Joy! Oh, how wonderful! Bliss! Ice Cream!


Suppose there was a magical way of knowing when an email was read. What are some of the reasons for people to be interested in knowing when exactly an email was read?

  1. If you are a professional email writer, then, to know the quality of your email
  2. If you are an email marketer, to know the impact of your email
  3. If you are using a new technology to send emails in bulk, to know whether those emails are reaching the audience at all.
  4. To optimize subject line
  5. To not worry needlessly about content, when the email was not even opened!


So many CRM companies routinely know whether an email was opened. How do they do this magic? The proper way is to “request read receipt” that is offered by Gmail / Outlook / Yahoo. But, those ask the reader a question on whether to send the read receipt – and the reader might say no! So, the CRM companies use a sneaky way to identify whether an email was read. How do CRM companies know an email was opened, even if the user does not send them “read receipt”?

The answer is through personalized 1×1 invisible images!

These invisible pixels are placed in the email, usually, towards the end. When the email client loads the email, it also tries to fetch the images. One of the images is the invisible one. So, if you could only know when a personalized invisible image was downloaded, you will know which of the users saw the email precisely when.

So, how can you know when an image was downloaded?

For this, you need to have your own image hosting server, that shares its HTTP access logs with you. Whenever an image is downloaded, the HTTP access log has a record, including the URL that was used to fetch the image.

If you sent an email to 100 people, you will need unique URL for image for each of the 100 people. Then, by examining the URL, you will know who opened the email when.


That was a whirlwind tour of concepts. We stayed at concepts and did not dive deep into how a server log looks like, or how the invisible image is composed. Those are good topics for another post. Here, we are now interested in understanding CRM systems, and what features they need to implement so that you can know which emails were opened.

What are the software components that a CRM system needs to implement for tracking which emails were opened?

  1. Generate a unique image URL for each user
  2. Maintain a mapping-table of user, email-details, and open-tracking-URL
  3. Host a web server that serves images
  4. Periodically read the access logs from the web server
  5. Extract timestamp and URL from the access logs
  6. Translate URL to user and email-details by looking up the mapping-table
  7. Publish a report with the updated information.


That is it! An invisible pixel in the email will prevent the agony of knowing whether an email was opened. This technology is used only by CRM companies which can justify the investment in hosting their own image server. Perhaps there is a business idea possibility for everyone else?

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