How accurate are email open rates generally?

Email open rates are generally not 100% accurate. They are tracked using a tracking pixel which registers an open when loaded. Factors like image blocking, spam filters pre-fetching emails, and privacy features (e.g., Apple Mail Privacy Protection) can all lead to either undercounting or overcounting actual human opens.

Does Gmail image caching inflate my unique open rates?

For unique (first) opens, Gmail's image caching actually tends to make the data more accurate . Since images are displayed by default via Google's proxy, the tracking pixel is more likely to fire, ensuring opens are counted even if a user had images previously disabled. However, it does prevent accurate tracking of repeat opens since subsequent views are served from the cache.

What other factors affect email open rate accuracy?

Besides Gmail caching, factors include automated pre-fetching by spam filters or security scanners, Apple Mail Privacy Protection (MPP) that pre-loads all content, and email clipping if the tracking pixel is at the bottom of a long email.

Should I stop tracking open rates altogether?

No, you shouldn't stop tracking open rates entirely. Despite their inaccuracies, they remain a valuable indicator of email program health and audience engagement trends . It's crucial to view them in context, alongside other metrics like click-through rates and conversions, to get a holistic view of your campaign performance.

How can I get more accurate email engagement data?

To get more accurate engagement data, focus on metrics that require active user interaction, such as clicks on links within your emails and ultimate conversions (e.g., purchases, sign-ups). These actions are less affected by automated processes. Also, segment your audience by email client to understand how different providers impact your metrics .

How accurate are email open rates and how does Gmail image caching affect them? - Technical - Email deliverability - Knowledge base

Email open rates have long been a cornerstone metric for marketers to gauge campaign performance and subscriber engagement. We often rely on these numbers to understand if our messages are resonating and if our email deliverability is on point. However, the accuracy of these rates, especially concerning providers like

Gmail, is frequently questioned. Many factors can influence how opens are tracked, leading to discrepancies that can skew our understanding of performance.

The primary method for tracking email opens involves a tiny, invisible image, often called a tracking pixel, embedded within the email. When an email client loads this pixel, it registers an open. But what happens when an email provider like Gmail implements image caching? How does this impact the data we rely on, and are our open rates truly reflective of engagement?

How email open tracking works

To understand the nuances of email open rates, we first need to look at the fundamental mechanism behind them. Most email service providers (ESPs) embed a transparent, 1x1 pixel image into every email. When a recipient opens the email and their email client downloads images, this pixel is loaded from the ESP's server. This load is then recorded as an email open.

However, this method has inherent limitations. Historically, if a user had images disabled by default in their email client, or if an email was clipped due to its size, the tracking pixel might not load, leading to an undercount of actual opens. This is why it's always been advised to view open rates as an indicator of engagement trends rather than a precise count of individual interactions. You can learn more about if Gmail accurately tracks email opens in our dedicated article.

Despite these challenges, open rates remain a useful metric for gauging the health of your email program, especially when looking at patterns over time. A consistent drop in open rates for Gmail users, for instance, could signal broader deliverability issues or content fatigue, prompting me to investigate further.

Gmail's image caching explained

In 2013, Gmail introduced a change that significantly impacted how images are handled: all images in emails are now displayed by default, and they are served through

Google'ssecure proxy servers. This means that when a user opens an email, even if they previously had images blocked, Gmail automatically downloads and caches these images on its servers. The next time the user opens the same email, the images are served from Google's cache, not from the original sender's server.

Many marketers initially worried that this change would inflate open rates or make them less accurate. The reality is more nuanced. For unique opens, Gmail's caching actually makes the tracking more reliable. Since images are loaded by default, the tracking pixel is almost guaranteed to fire on the first open, even if the user hasn't explicitly enabled images. This means that previously invisible opens (where a user read the text-only version) are now counted, potentially leading to a slight increase in reported unique open rates. In this sense, it can improve the accuracy of unique open tracking for Gmail users.

The main impact of Gmail's image caching is on repeat opens. Since images are cached after the first view, subsequent opens of the same email by the same user will not trigger another pixel load from your ESP's server. This means your data will accurately reflect unique opens but will not show how many times a user reopened an email. This is a crucial distinction to make when evaluating your metrics and understanding the impact of Gmail's image proxy.

Unique vs. repeat opens

Gmail's image caching primarily affects the tracking of repeat opens. The first time a

Gmail user opens an email, the tracking pixel is loaded, and a unique open is registered. Subsequent opens of the same email will fetch images from Google's cache, not your server, so they won't register as new opens.

Beyond Gmail: other factors affecting accuracy

While Gmail's caching influences repeat open tracking, it's just one piece of the puzzle. Other factors can also lead to inaccuracies (or perceived inaccuracies) in your email open rates, making it essential to have a comprehensive view of what affects this metric.

One common issue is automated activity from spam filters and security scanners. Many inbox providers and corporate security systems will pre-fetch all links and images in an email to scan for malicious content before delivering it to the recipient's inbox. This can trigger the tracking pixel, registering an open even if the human recipient never actually saw or interacted with the email. These false opens can inflate your open rates, giving a misleading impression of engagement.

Another significant development is

Apple'sMail Privacy Protection (MPP), introduced with iOS 15. Unlike Gmail, which caches images on the first *actual* open,

Apple Mail pre-fetches and caches all images, including the tracking pixel, as soon as an email arrives in the inbox, regardless of whether the user actually opens it. This has led to significantly inflated open rates for Apple Mail users, making open rates an even less reliable indicator of true engagement for a segment of your audience. If you want to know more about this, check out our guide on how to estimate real open rates with Apple Mail Privacy Protection.

Gmail image caching

Purpose: Enhances security and privacy for users, speeds up image loading for subsequent opens.

Impact on unique opens: Generally improves accuracy because images are loaded by default on the first open, even if not explicitly enabled by the user.

Impact on repeat opens: Subsequent opens fetch images from Google's cache, not your server, so repeat opens are not tracked.

Apple mail privacy protection (MPP)

Purpose: Enhances user privacy by masking IP addresses and pre-loading all remote content.

Impact on unique opens: Leads to inflated open rates as images are pre-fetched upon arrival, regardless of actual user engagement.

Impact on repeat opens: Similar to Gmail, subsequent opens are likely served from cache and not tracked.

The placement of your tracking pixel within the email can also affect its accuracy. If the pixel is at the very bottom of an email that frequently gets clipped by email clients due to size limitations, the pixel might not load, leading to an undercount of opens. This is something I've seen firsthand, and it's why monitoring how Gmail email clipping affects deliverability is important.

Ultimately, open rates are a dynamic metric influenced by various technical and user-side factors. While

Gmail's image caching primarily affects repeat opens, the broader landscape of email privacy features and security measures means that relying solely on open rates for campaign success can be misleading.

Factor	Impact on open rates	Notes
Gmail image caching	More accurate unique opens; no repeat opens tracked.	Images served via Google's proxy after first open.
Apple Mail Privacy Protection (MPP)	Inflated unique opens due to pre-fetching.	All images loaded upon arrival, regardless of user interaction.
Spam filters/security scanners	False opens from automated pre-loading.	Bots or servers accessing links/images to scan content.
Email clipping	Underreported opens if pixel is at the clipped bottom.	Large emails exceed client display limits, hiding content.

Rethinking your metrics

Given the complexities of open rate tracking, it's clear that focusing solely on the raw number can be misleading. Instead, I find it more valuable to look at trends over time. Are your open rates consistently rising or falling for specific segments or campaigns? This trend data can provide much more actionable insights into your audience's engagement and the overall health of your email deliverability.

Moreover, I always recommend prioritizing other engagement metrics, such as click-through rates (CTR) and conversions. A click signifies active interest, and a conversion directly ties back to your business goals. These metrics are less susceptible to the automated pre-fetching that affects open rates, offering a more reliable picture of true subscriber interaction. Understanding how to increase email click-through rate is often more impactful.

While Gmail's image caching does affect the granular tracking of repeat opens, it generally leads to more accurate unique open reporting for its users by ensuring images load by default. The real challenge to open rate accuracy comes from broader privacy initiatives and security scans that pre-fetch emails. By understanding these technicalities and shifting focus to more reliable engagement metrics like clicks and conversions, we can still gain valuable insights from our email campaigns.

Views from the trenches

Best practices

Always view open rates as a directional indicator, not a precise measure, focusing on trends over time.

Prioritize clicks and conversions as primary KPIs, as they reflect deeper engagement and business impact.

Ensure your tracking pixels are placed optimally within the email, avoiding areas prone to clipping.

Understand the nuances of different email clients (like Gmail vs. Apple Mail) regarding image loading and privacy features.

Common pitfalls

Over-relying on raw open rate numbers as the sole indicator of campaign success, leading to misinterpretations.

Ignoring the impact of spam checkers and security tools that can trigger false opens.

Not accounting for email clipping, which can lead to underreporting of opens if the pixel is at the bottom.

Comparing open rates across different email clients or infrastructure without understanding their varying tracking methods.

Expert tips

I recommend tracking conversions or failed conversions directly from your email links, as these are quantifiable metrics that truly matter.

Consider the location of your tracking pixel within the email; if it's at the bottom, it might not load if the email is clipped or closed quickly.

Open rates are more accurate than broad media metrics, like TV ad views, but still have limitations.

Look for trends in open rates to assess the relative health of your email program or specific campaign types.

Expert view

Expert from Email Geeks says open tracking links, including those to images, are typically serialized so they cannot truly be cached.

2019-11-20 - Email Geeks

Expert view

Expert from Email Geeks says open tracking should be considered a rough indicator of activity, as it is not entirely accurate due to various cases where automatic image opening is disabled by users or webmail providers.

2019-11-20 - Email Geeks