How accurate are email open rates and how does Gmail image caching affect them?

Key findings

• Image caching impact: Gmail's image caching (prefetching) generally means that open tracking pixels are loaded more reliably. This can lead to a more accurate representation of unique opens compared to a time when images were blocked by default. However, it can also lead to artificial opens triggered by security scanners or prefetching mechanisms before a user genuinely views the email.
• Serialised links: Open tracking links, including those for images, are typically serialised. This means each link is unique per recipient, preventing widespread caching that would skew individual open metrics.
• Open rate as an indicator: While not perfectly precise for individual opens, open rates remain a valuable metric for tracking trends in engagement and assessing the overall health of an email program over time. They are more reliable when compared across campaigns or audience segments rather than as an absolute measure.
• Disabling images: Some users or webmail providers disable automatic image loading, which can lead to undercounted open rates if the tracking pixel (often a tiny image) is not loaded. Gmail's default behavior, however, has mitigated this for its users.
• Spam checkers: Automated spam checkers often request all email assets, including tracking pixels, which can artificially inflate open rates by registering an 'open' without actual human interaction. This is a common factor in discrepancies.

Key considerations

• Focus on trends: Rather than obsessing over the exact percentage, monitor open rate trends to identify improvements or declines in engagement. Sudden drops or spikes can indicate deliverability issues or changes in audience receptiveness.
• Beyond opens: Prioritize more definitive engagement metrics like click-through rates (CTR) and conversions. These provide a clearer picture of recipient interest and action, which are directly tied to business objectives. Tracking conversions or failed conversions is often more quantifiable.
• Pixel placement: The placement of the tracking pixel within an email can affect reported opens. If the pixel is at the very bottom, it may not load if the email is clipped or closed before fully rendering.
• Deliverability insights: While not perfect, opens can still provide valuable insights into deliverability. A client seeing significantly lower Gmail open rates compared to other providers or their historical performance might indicate a deliverability problem affecting inbox placement.

Key opinions

• Inflated metrics: Many marketers report that a significant portion of emails sent to Gmail or G Suite recipients show false opens, due to prefetching and security scans, which has been a consistent trend over the years.
• Improved accuracy for unique opens: Some believe Gmail's default display of images can actually improve the accuracy of statistics for unique message opens, as previously invisible opens are now tracked.
• General inaccuracy: It's a commonly accepted notion that email open rate reporting can be off by as much as 35%, making it a misleading metric for precise measurement.
• Focus on conversions: Many marketers advocate for prioritizing conversion metrics over open rates, as conversions (e.g., purchases, sign-ups) directly reflect business goals and are less susceptible to false positives.
• Trend analysis: Open rates are still considered valuable for observing trends over a series of emails or assessing the relative health of an email program, rather than for granular, absolute figures.

Key considerations

• Engagement signals: Even with inaccuracies, sustained open rates can serve as a positive signal to Internet Service Providers (ISPs) about subscriber interest, potentially aiding deliverability. Low engagement can negatively impact sender reputation.
• Content quality: Focus on delivering valuable content to drive genuine engagement, which in turn leads to more reliable metrics. Quality content encourages more actual opens and clicks.
• Campaign comparison: Use open rates to compare the performance of different campaigns or subject lines within your own email program, rather than comparing to industry benchmarks that may not account for diverse tracking methodologies. Open rate reporting can be off by a significant margin.
• Holistic view: Combine open rate data with other metrics, such as click-through rates, bounce rates, and unsubscribe rates, for a comprehensive understanding of email performance. This multi-metric approach helps to paint a more accurate picture of engagement.
• Client reassurance: It's important to educate clients that Gmail image caching generally does not negatively impact open rate tracking reliability, and in some cases, may even improve it by ensuring images are loaded by default.

Key opinions

• Not perfectly accurate: Experts agree that open tracking, especially of images, is not perfectly accurate due to various factors like automatic image loading being disabled or enabled by default by email clients or users.
• Focus on conversions: The primary metric that truly matters is often conversions or failed conversions (e.g., successful orders). These are quantifiable and directly impact business outcomes, providing a much clearer picture of email effectiveness.
• Open rates as indicators: Open rates should be treated as a rough indicator of activity, useful for observing trends over time and assessing the general health of an email program, rather than as a precise measure of individual engagement.
• Spam checker influence: Automated spam checkers and security software often request all assets, including tracking pixels, which can artificially trigger 'opens' without human interaction, further skewing the data.
• Serialised links: The serialisation of open tracking links (including those for images) typically prevents widespread caching from distorting individual open counts, as each link is unique to the recipient.

Key considerations

• Look at trends, not absolutes: The most effective use of open rates is to observe trends. A consistent decline or a sudden drop in open rates for a specific campaign or client, especially at Gmail, can signal underlying deliverability issues. Changes in trends are critical signals.
• Pixel placement matters: Consider the placement of the tracking pixel within the email. If it's at the very bottom, it might not load if the email is clipped or closed prematurely, leading to underreported opens. This can impact email tracking pixel deliverability.
• Deliverability diagnostics: While open rates don't define business success, they are a valuable diagnostic tool for deliverability. A poor open rate, particularly compared to historical data or other ISPs, can indicate inbox placement problems that need investigation.
• Compare apples to apples: Be cautious when comparing open rates across different email service providers (ESPs) or infrastructures, as tracking methodologies can vary significantly. This can lead to misleading comparisons and incorrect conclusions about performance.
• Content quality and frequency: Regardless of tracking nuances, the fundamental strategy remains to send valuable content frequently enough to engage the audience. This drives genuine interaction (clicks, conversions) which is more reliably tracked and positively impacts domain reputation.

Key findings

• Image proxying: Gmail loads all images through its own secure proxy servers. This means the images are cached on Google's servers, and subsequent loads of the same image from the same recipient come from the cache, not directly from the sender's server. This helps protect user privacy and security.
• Default image display: Gmail automatically displays images by default, which can lead to higher reported open rates. Previously, users had to click 'display images,' which often resulted in undercounted opens if the tracking pixel wasn't loaded.
• Impact on unique opens: The automatic display of images generally improves the accuracy of unique open rates for Gmail recipients. Opens that would have been missed when images were blocked are now recorded.
• Security vs. tracking: Gmail's image caching policy prioritizes user security (e.g., preventing tracking of IP addresses, location) and performance over precise, individual open tracking by marketers. This is a trade-off that impacts data granularity.
• Prefetching: Gmail may prefetch images from emails even before a user explicitly opens them, particularly under certain conditions, which can lead to 'false' opens being recorded if a tracking pixel is part of the prefetched content.

Key considerations

• Focus on unique views: While Gmail's caching might cause some 'false' opens, the automatic display of images means that actual unique views are more likely to be counted, reducing the previous problem of undercounting legitimate opens.
• Reduced tracking opportunities: Marketers may experience reduced tracking opportunities regarding precise geolocation or subsequent opens by the same user, as images are served from Google's proxies, not directly from the sender's server. Image caching affects email marketing tracking.
• Adapt analytics: Marketers should adjust their analytics expectations, recognizing that 'opens' from Gmail may include prefetch activity or security scans. Emphasis should shift to other engagement metrics like clicks.
• Privacy implications: The caching behavior is fundamentally a privacy feature, protecting recipients from malicious tracking pixels or revealing their IP addresses. This enhances the user experience at the cost of some marketer tracking capabilities.
• Deliverability not jeopardized: Gmail's image caching doesn't inherently harm email deliverability. Instead, it's a standard behavior for major ISPs designed to optimize email loading and enhance security for their users. It doesn't affect Google Postmaster Tools IP reputation.