Pardot Knowledge Base

How are HTML opens measured?

Last Updated: Jan 23, 2017 | Print this Article

Open rates are difficult to measure accurately because they are tracked based on an image loading in the recipient's inbox. In most email browsers, including Microsoft Outlook, image loading is turned off by default. This is an unfortunate limitation of technology and often results in the number of HTML opens displayed in an email report being quite a bit lower than the actual number of views.

Why open rates aren't always an accurate reflection of email interaction

Here are a few examples of why open rates aren't always an accurate reflection of how prospects interact with your emails:

  • Because we can't insert our tracking pixel into text emails, we can't record email opens unless a prospect clicks a tracked link in a text email. If a prospect clicks a tracked link in your text email, Pardot will record the click, and an HTML email open.
  • Some automated spam checkers and virus scanners can trigger multiple email opens when they scan an inbox. These opens show up as HTML opens on prospect records, and they can usually be identified because the opens occur in a short period of time.
  • If an email client downloads images by default and the recipient uses a preview pane to scroll through the inbox, an email viewed briefly in the preview will be counted as opened even if the content was not read.
  • If an email client blocks images by default, a recipient could potentially open an email, read it and even click on a link without downloading the images. If the recipient clicks on a link within the email, we will infer that they had to open the email and record an open in their activities (and run any completion actions) even if they do not download the images.

A better solution is to measure the success of your message by tracking clicks and unique clicks, which are also displayed in your email report. This number serves as a more accurate indication of how effective your call to action was and also allows you to quickly view a list of prospects who responded to your messaging.

How does this relate to prospect activities?

If a recipient does not download images in an email you sent them and does not click on any tracked links within the email, their prospect activity report will not show an email open, even though they may have opened and read the email.

Sometimes a prospect who did not load images may click on a tracked link or paste the URL from a text-only email directly in their browser. In these cases, the prospect activity report will show an email tracker "click" as well as an "open" (since it's clear they opened the message even though they did not download images).

Email Open Click Activities

Why wasn't my HTML email open recorded?

Pardot's email reports will not display HTML email opens when:
  • An email is text only, and the prospect did not click any tracked links
  • An email is sent through an email plug-in
  • An email does not contain a </body> or </html> tag
    • Pardot adds tracking images right before the </body> tag that are required for HTML reporting to function and report accurate numbers
    • Emails without body tags will also have higher spam scores in certain spam filters, especially SpamAssassin
    • Pardot automatically inserts the correct body tags into any HTML emails designed using the graphical editor
  • An email is sent while your CNAME is incorrect
    • Requests to download email images are sent to your CNAME, which then redirects to If your CNAME is incorrect or does not point to, our servers will not receive the request and we will be unable to record email opens.

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