What's an Email Tracking Domain?

A Letter in the Void

Write a long heartfelt letter to a loved one, tuck it into a bottle and violently hurl it out into the cold uncaring sea.

Do that and you'll have a good sense of how marketers feel when they hit the send button on their email campaigns.

Which is why analytics are so important, the two most important metrics being:

  1. How many people opened the email.
  2. How many people clicked a link in the email.

By collecting these fairly basic metrics, you can find out so much. Did people respond to your subject? Were they interested in what you had to say? What can you do better next time?

This collection is mostly done with tracking domains - a tool for collecting email metrics.

What is a Tracking Domain?

A Tracking Domain is the URL used for analytics collection within your emails. In the same way that www.hubspot.com points to the main Hubspot Website, a tracking domain like: tracking.some-email-service.com points to the web application set up by the Email Service, to collect email opens and click through information for the campaigns sent through their service.

Can a Recipient/Subscriber See the Tracking Domain?

In most cases, a subscriber who receives an email from you won't directly see the tracking domain. The two exceptions are:

  1. When hovering over a link on Desktop.
  2. When clicking a link within the email

On the Desktop, the status bar in the lower portion of the browser will display the URL that the link points to:

When a recipient clicks on a link in an email you sent them, they'll first be sent to the tracking server. This will record which link, when they clicked it, etc. If their Internet connection is slow, the tracking server is slow, the site you're linking to is slow, or any other general network weirdness, then the user will quite likely see the URL of the tracking server.

Why Would I Want a Custom Tracking Domain?

It's probably an understatement to say that most of your email subscribers don't fully grasp how email marketing works. Not that they're unintelligent, but simply that they have a million more pressing things on their mind. So when in the midst of clicking on something they need in your email, if they see a wildly unfamiliar name of some service appear, they may think that:

  • You're doing something bad with their account.
  • The email is fake or a phishing attempt.
  • Something has gone wrong.

Or they might even simply be slightly confused and put off by some "Mail Monkey" looking at the links they click on in an email.

Setting up a custom tracking domain will help smooth over any questions by inserting your own branded sub-domain instead of the email services domain.

So, https://tracking.example-email-service.com becomes https://track.my-cool-shop.com - and provides a better experience.


Where Do Tracking Domains Fit in the Email Creation?

It's entirely possible to be a productive email marketing professional and never worked directly with an email tracking domain, as many email services will transparently take care of tracking for you.

The typical flow of events is:

  1. You'll write and design your email.
  2. You'll use the Subject Line Analyzer.
  3. After some Preview and Testing you'll Send.
  4. The Email Service will rewrite the HTML and Text versions of your email so that:
    • An image tag from the tracking domain is included.
    • Links in the email can have their clicks collected.

Typically the Tracking Domain links will not be present in most previews or sanity checks (when you send yourself a copy of the email) - and will only be inserted into the final email send.

How Does a Tracking Domain Collect Metrics?

It would be great if there was such a thing as a Magic Metric Fairy that would travel around to data centers all over the earth, depositing nicely collated reports of email activity. Unfortunately, we live in a Muggle world and must rely upon the technology for our analytics gathering.

Collecting Email Open Rate Data

While there are a few other methods, the primary (and most reliable) means of determining if an email has been opened is with a tracking image. These used to be 1px by 1px invisible gifs or other similarly unnoticeable images. Now, most tracking just references an image src that's never loaded.

If you looked at the HTML of a tracked email somewhere in it you'd see something like:

<img src="https://tracking.email-service.com/20303493024">

Which when loaded in an email client would "tell" the server at tracking.email-service.com that the contact number 20303493024 had opened the email.

Collecting Link Click Data

When you create your emails you add links for all sorts of things: Calls to Action, Support Requests, Items on Sale, etc.

When you're setting up the email, the URLs in your links look something like:


When the tracking domain links are inserted this will be transformed into:


People clicking the link will first hit the tracking server of your email service, their click recorded and then they'll be redirected to the URL you'd specified.

If you are using a custom domain for your tracking server the link tag will look more like:


Tracking servers forward all parameters sent in, so your UTM campaign codes, item IDs and extra reference codes should all be preserved.

How Do You Assign a Custom Domain to the Tracking Service?

You should follow the specific instructions given to you from your email service (we've listed some below) but in general you set up a particular type of DNS record called a CNAME.

If you don't already have access to your domain's DNS Server you'll need to work with your IT staff on the project.

What's a CNAME Record?

A DNS CNAME is sometimes called an alias record as it's providing an alternate name for a particular server. Unlike forwarding a user from one site to another (which would show the domains to the user), a CNAME hides the aliased server. It should be noted that it's trivial to look up what a CNAME record is pointed to.

This isn't a security measure and from a technical standpoint everything works exactly the same. The only difference is that instead of a potentially confusing domain being shown to your email recipients, your nicely branded domain is shown instead.

Example CNAME Setup

The image below is from our DNS Provider's (DNSimple) management screen. You're likely using something different, but the configuration should be very similar.

What Should I Name My Custom Tracking Domain?

At first glance it might seem like any name is as good as any other for your tracking domain, but there are a couple things to consider:

Ad Blockers

Ad blockers work off of regular expressions (patterns) - many of which are incredibly simplistic and will block anything with a matched pattern. It is trivially easy to accidentally create a custom tracking domain that matches a known blocking pattern. You should test your domain against both uBlock Origin and Ad Block Plus (with private tracking enabled).


Some users are sensitive to being tracked unnecessarily - so choose a custom domain that builds trust and doesn't turn people away.

Wrapping it Up

Tracking Domains are an essential tool in collecting analytics and building emails that your recipients actually want to receive. You should understand how they work in case you get questions from subscribers about these "weird domains" in your emails. If at all possible you should setup a Custom Tracking Domain as it's free and can only help the effectiveness of your email campaigns.

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