How to track email open to close time or reading duration in emails?
Michael Ko
Co-founder & CEO, Suped
Published 10 Aug 2025
Updated 18 Aug 2025
7 min read
For email marketers and deliverability professionals, understanding how recipients engage with emails is crucial. We track opens, clicks, and conversions, always seeking deeper insights. One metric that frequently comes up in discussions is the desire to track the exact open-to-close time or reading duration of an email.
The idea is compelling: imagine knowing precisely how long someone spent reading your newsletter or sales pitch. This granular data could inform content strategy, design choices, and even send times. It seems like the holy grail of email engagement.
However, the reality of email technology, privacy measures, and diverse email clients makes true open-to-close time tracking incredibly difficult, if not impossible, to achieve with consistent accuracy across the board. While some email clients and platforms offer limited metrics, a universal, precise measurement remains elusive.
Technical limitations of current tracking methods
Most email tracking relies on a tiny, invisible 1x1 pixel image embedded in the email's HTML. When the recipient opens the email and their email client loads images, this pixel is fetched from a server, registering an open event. This method, while widely adopted for open rates, has significant limitations when it comes to measuring reading duration.
A major challenge is image caching and pre-fetching by internet service providers (ISPs) and email clients. For example, Gmail often caches images when an email arrives, triggering an open event before the user has even seen the email. This means the open timestamp is not necessarily when the user *starts* reading. Similarly, there's no reliable signal for when a user *closes* an email or navigates away.
Furthermore, many email clients block images by default for privacy or security reasons, requiring users to manually enable them. If images aren't loaded, the pixel-based open isn't registered at all. This also affects the ability to get an accurate read receipt or time duration for engagement. Some have attempted alternative tracking mechanisms for government emails where traditional tracking is unreliable.
Because of these factors, an email open as reported by a tracking pixel should be viewed as an indicator of interest, not a precise measure of when a person starts reading or for how long. The nuances of how email clients track opens can significantly skew any attempt to derive a reading duration metric directly from open and close events.
Attempts at measuring reading duration
Despite these challenges, some providers and platforms have attempted to offer estimates of reading duration. One notable example often cited is the approach used by Litmus, which historically included engagement metrics. These methods typically involve clever techniques like continuously loading pixels or CSS-based tricks, but they come with their own set of caveats.
For instance, some try to use a streaming pixel that theoretically continues to load, allowing for a duration measurement. However, this is heavily dependent on the email client's rendering behavior, network conditions, and whether the client actually keeps the image stream active. As email clients evolve and proxies become more prevalent, the reliability of such techniques diminishes over time.
AMP (Accelerated Mobile Pages) for email offers more dynamic capabilities and could, in theory, enable more sophisticated tracking of user interactions within the email itself. However, AMP email adoption is not universal, and its interactive components introduce complexity. The vast majority of emails still rely on standard HTML, limiting the scope for advanced, browser-like tracking within the email client.
Ultimately, while the pursuit of precise reading duration is understandable, the current email ecosystem presents significant hurdles. It's more practical to focus on metrics that are reliably measurable and provide actionable insights into recipient behavior.
Traditional open tracking
Relies on a 1x1 pixel image loading to register an open. It provides a timestamp for when the email was 'opened' (i.e., when the pixel was fetched).
Impacted by image blocking, pre-fetching by ISPs and email clients, and caching services. This means the 'open' time often doesn't align with actual user engagement.
Cannot reliably determine when a user stops reading or closes the email, making duration measurement speculative.
Focusing on actionable engagement metrics
Given the inherent limitations of tracking email open-to-close time, I find it more productive to focus on metrics that truly indicate user interest and engagement. These are often actions that recipients take *after* opening an email.
The most significant of these is click-through rate (CTR). If a recipient clicks a link within an email, it's a clear signal that the content resonated enough for them to take the next step. This is a far more reliable indicator of active engagement than a speculative reading duration. You can learn how to increase email click-through rate through various strategies.
Other valuable engagement metrics include replies to an email, forwards, and direct conversions (like purchases or sign-ups) that originate from email campaigns. These actions confirm that your message not only reached the inbox but also spurred meaningful interaction. Providers like HubSpot and Salesforce provide robust tracking for these kinds of interactions, offering more clarity than trying to estimate how long someone was looking at your email. You can also explore alternative metrics to open rates for measuring engagement.
Understanding how ISPs track email engagement is key, as their methods impact deliverability. They often prioritize actions like clicks, replies, and whether an email is moved to a priority inbox over simple opens, especially with the rise of automated image loading. For more in-depth insights into email reputation, you can explore how to accurately measure email engagement despite potential issues like bot clicks.
Advanced approaches and future outlook
Understanding open time
The open event is recorded when the tracking pixel loads. This can be influenced by mail client settings, Outlook's reading pane, and security features that may pre-fetch or block images.
An email could be marked as 'opened' even if the user never actively engages with it, for example, if an anti-spam scanner opens it.
While direct open-to-close time remains challenging, some advanced approaches aim to provide deeper insights into engagement. These often combine traditional tracking with more sophisticated methods or focus on specific, controlled environments.
For platforms capable of handling AMP for Email, the interactive nature allows for more granular event tracking within the email client itself. This could include scroll depth, time spent on specific sections, or interactions with embedded forms. However, this relies on both the sender and recipient's email client supporting AMP, which is not yet universal. When a recipient clicks a link from within the email's reading pane, it still counts as a tracked click, offering more concrete engagement data.
Looking ahead, as privacy regulations evolve and email client behaviors change, the reliance on traditional pixel-based open tracking may continue to diminish. This reinforces the need for marketers to adapt and focus on more robust and privacy-friendly engagement metrics. Some even argue that email tracking, as we know it, is dead, prompting a shift in focus to other reliable indicators.
Rethinking email engagement metrics
While tracking email open-to-close time or reading duration is a challenging goal due to technological and privacy limitations, focusing on actionable engagement metrics like clicks, replies, and conversions provides more reliable and meaningful insights. It's about adapting our measurement strategies to the evolving landscape of email.
Views from the trenches
Best practices
Actively monitor engagement beyond opens by focusing on clicks, replies, and direct conversions, as these are more reliable indicators of recipient interest.
Segment your audience based on their engagement patterns, rewarding highly engaged recipients with tailored content and special offers.
Use email authentication protocols like SPF, DKIM, and DMARC to build trust with ISPs and improve deliverability, ensuring your emails reach the inbox where engagement can occur.
Regularly clean your email lists to remove inactive subscribers and spam traps, which can negatively impact your sender reputation and overall deliverability (or risk getting added to a blocklist).
Common pitfalls
Over-relying on pixel-based open rates as the sole measure of engagement, as image caching and privacy features can skew these numbers.
Attempting to implement complex 'streaming pixel' or CSS-based hacks for reading time, which are often unreliable across diverse email clients and may trigger spam filters.
Failing to adapt measurement strategies as email client technologies and privacy standards evolve, leading to outdated or inaccurate insights.
Ignoring other important deliverability signals, such as bounce rates and spam complaints, which are often more indicative of sender reputation than speculative reading times.
Expert tips
Consider using AMP for Email components for specific, highly interactive campaigns where you need granular engagement data, understanding its limited support.
Focus on optimizing your email content and calls to action (CTAs) to drive measurable clicks and conversions, which are undeniable proof of engagement.
Invest in understanding your audience's preferences for email content format and frequency, as this directly influences their likelihood to engage deeply with your messages.
Regularly check if your domain or IP is on any email blocklist (or blacklist), as this directly impacts whether your emails are even seen, let alone read.
Marketer view
Marketer from Email Geeks says that Litmus used to offer analytics that measured engagement, though its effectiveness has varied over time.
2024-07-15 - Email Geeks
Marketer view
Marketer from Email Geeks says that pixel-based reading time tracking was more common in the past but has become less useful due to modern email client changes and the prevalence of proxy servers.
Gmail often caches images when an email arrives, triggering an open event before the user has even seen the email. This means the open timestamp is not necessarily when the user *starts* reading. Similarly, there's no reliable signal for when a user *closes* an email or navigates away.
Litmus, which historically included engagement metrics. These methods typically involve clever techniques like continuously loading pixels or CSS-based tricks, but they come with their own set of caveats.
HubSpot and Salesforce provide robust tracking for these kinds of interactions, offering more clarity than trying to estimate how long someone was looking at your email. You can also explore alternative metrics to open rates for measuring engagement.
Outlook's reading pane, and security features that may pre-fetch or block images.
