I'm relatively new to HTML Email Development, and I'm trying to improve my understanding of HTML Email structures by dissecting HTML Emails on "reallygoodemails.com."
On the example located at this address: "https://reallygoodemails.com/emails/craving-some-chocolate/live" , there is an IMG tag located on line "502" directly after the body tag in the preheader section of the HTML Email.
What does this IMG tag do?
It's a Spy Pixel.
Spy pixels or tracker pixels are hyperlinks to remote image files in HTML email messages that have the effect of spying on the person reading the email if the image is downloaded. They are commonly embedded in the HTML of an email as small, imperceptible, transparent graphic files. Spy pixels are commonly used in marketing, and there are several countermeasures in place that aim to block email tracking pixels. However, there are few regulations in place that effectively guard against email tracking approaches.
To summarize, when the email is opened and the browser loads that image, the browser will look up that URL expecting image data. However, the image data is 0 pixels by 0 pixels, so the email doesn't display anything. Instead, the server hosting that "image" knows you opened the email. Because the URL is unique to your email address, they know that you personally opened the email. That information is useful for showing the sender how their email marketing campaign is performing.