How do tracking pixels in HTML emails work and can they be removed?

Key findings

• Functionality: Tracking pixels are typically 1x1 transparent images embedded in an email's HTML code. When an email client loads this image, a request is sent to the sender's server, which logs the open event, IP address, and sometimes other data like client type or location. For more on this, see our article on how email tracking pixels affect deliverability.
• Deletion misunderstanding: The act of deleting an email from a user's inbox does not delete the tracking pixel from the sender's server. The pixel is a remote resource, and the tracking event has already occurred once the image was loaded, regardless of the email's subsequent local status.
• Client-side blocking: The most effective way for recipients to 'remove' the effect of tracking pixels is to prevent images from loading automatically in their email client. Most modern email clients, like Gmail and Outlook, offer settings to block external images by default, requiring user permission to display them.
• Privacy features: Newer privacy features, such as Apple's Mail Privacy Protection (MPP), further obscure tracking pixel effectiveness by pre-loading images through proxy servers, making it difficult for senders to identify actual opens or recipient IP addresses. Learn more about how MPP and ITP affect tracking.

Key considerations

• Impact on metrics: The widespread blocking of images means that email open rates, when measured solely by pixel loads, are increasingly inaccurate. Marketers should consider alternative metrics beyond pixel-based opens to gauge engagement. Read more on how to stop email pixel trackers.
• User control: Recipients have significant control over pixel tracking through their email client settings. Educating users about these options empowers them to manage their privacy.
• Alternatives for senders: For senders, relying solely on tracking pixels for engagement metrics is becoming less reliable. Focusing on link clicks, conversions, or direct replies offers more accurate insights into recipient interaction. This is especially true for businesses, as described in our guide on emails without tracking pixels improving response rates.
• Data privacy: The use of tracking pixels raises privacy concerns, prompting both email clients and users to seek ways to mitigate unwanted surveillance. This reflects a broader trend toward greater data privacy in online communications.

Key opinions

• Open rate reliance: Many marketers still view open rates, derived from tracking pixels, as a key performance indicator, despite growing awareness of their inaccuracies due to privacy features.
• Misconceptions about deletion: A common misconception among some senders is that deleting an email removes the tracking pixel from existence, when in reality, the tracking event has already been recorded server-side once the image loaded.
• Pixel persistence awareness: Experienced marketers understand that the data collected by pixels resides on the sender's server, independent of whether the recipient keeps or deletes the email locally.
• User behavior: Some marketers acknowledge that many users do not regularly delete emails, contributing to a vast archive of digital data on email servers, including potentially loaded pixels.

Key considerations

• Adapting to privacy: Marketers are increasingly challenged to adapt their measurement strategies as email clients implement more robust privacy features that impact pixel-based tracking. For more information, read what Gmail's hidden images message means.
• Alternative metrics: There's a growing need for marketers to shift focus to more reliable engagement metrics, such as click-through rates and conversions, rather than solely relying on potentially inflated or inaccurate open rates from pixels.
• Transparency: Some marketers advocate for greater transparency with recipients about the use of tracking pixels, to build trust and manage expectations around data collection.
• Client settings: Marketers should be aware that recipients can easily disable pixel tracking through their email client settings, which directly impacts the accuracy of reported open rates. Understanding this can help explain discrepancies in campaign performance. How email tracking works offers more insight.

Key opinions

• Technical inaccuracy: Experts confirm that statements about pixels being 'deleted' when an email is deleted are technically incorrect, as the tracking event occurs when the image is loaded from the server.
• Data persistence: Once a tracking pixel loads, the data (e.g., open event, IP address) is recorded on the sender's server and remains there, regardless of whether the recipient deletes the email from their local inbox.
• Client-side control: The only effective method for recipients to prevent pixel tracking is through their email client's settings, specifically by preventing external images from loading automatically. This is a crucial distinction from simply deleting the email.
• Minimal storage impact: Experts note that even large archives of emails, including those with tracking pixels, consume a negligible amount of storage space, making the idea of deleting emails for space-saving irrelevant in modern contexts.

Key considerations

• Educating senders: There's a need to better educate email senders about the true mechanics of tracking pixels to prevent misinformation and foster more accurate data interpretation. For more, see our article on accurately measuring email open rates.
• Impact of privacy changes: Experts constantly assess how new privacy initiatives by email service providers (like Apple's MPP) impact the reliability of pixel-based tracking, influencing deliverability strategies. This impacts your overall email deliverability issues.
• User privacy controls: Understanding and promoting the use of email client settings for image blocking is crucial for users concerned about their privacy. Experts often recommend these settings as a practical defense against unwanted tracking. An article by Email on Acid delves deeper into tracking pixels.
• Shift to engagement metrics: The expert consensus points towards a future where marketers must increasingly rely on post-open engagement metrics, such as clicks and conversions, to accurately assess campaign performance.

Key findings

• Definition: A tracking pixel (or web beacon) is a small, usually 1x1 transparent GIF or PNG image embedded in HTML email code, designed to make a call to a remote server when loaded. For more about this, check out how tracking pixels compare to cookies.
• Mechanism: The pixel's source attribute contains a URL pointing to a server-side script. When the email client fetches this image, the server logs the request, capturing data such as the time of open, IP address, and sometimes user agent details.
• Embedded nature: Tracking pixels are integral parts of the email's HTML content, loaded as external resources. They are not stored locally with the email content itself after the initial fetch.
• Privacy controls: Documentation confirms that email clients prevent pixel tracking by not automatically downloading external images. This is the primary method of preventing the pixel from making its server call. This can also affect whether images in emails trigger spam filters.

Key considerations

• Incomplete data: Due to image blocking, pixel-based open rates provide an incomplete picture of email engagement. Senders must acknowledge this inherent limitation when analyzing campaign performance.
• Privacy compliance: The use of tracking pixels intersects with data privacy regulations, requiring senders to be transparent about data collection practices and offer recipients clear opt-out mechanisms or controls. The Federal Trade Commission highlights hidden impacts.
• Dynamic content: While simple pixels track opens, more sophisticated implementations can dynamically generate content or track other interactions based on recipient behavior, complicating simple 'removal' methods.
• Future of tracking: The evolution of privacy measures in email clients suggests that reliance on tracking pixels for open rates will continue to diminish, pushing the industry towards alternative, privacy-preserving measurement techniques.