Why do all-image emails sometimes have higher open rates?

All-image emails might show higher open rates because recipients are forced to load images to see any content, or due to automatic pre-fetching by email clients and security systems. This inflates the open count, as an 'open' is often just an image loading, not necessarily a sign of a human viewing the email.

Are open rates a reliable Key Performance Indicator (KPI)?

Open rates are increasingly unreliable as a primary KPI due to factors like Apple Mail Privacy Protection (MPP) and ISP pre-fetching, which artificially inflate numbers. They don't accurately reflect human engagement or campaign performance. For more information, read Is email tracking dead ?

What metrics should I focus on instead of open rates?

Focus on metrics like Click-Through Rate (CTR), Click-to-Open Rate (CTOR), conversion rates, and revenue. These indicate active engagement and direct business impact, providing a more accurate measure of your email campaign's success.

How do all-image emails affect deliverability and user experience?

Sending all-image emails can negatively affect deliverability by increasing the likelihood of being flagged by spam filters. They can also lead to poor user experience if images are blocked, and hinder accessibility for users with screen readers or visual impairments. Find out more about images in emails .

How can I accurately measure email campaign performance today?

Implement A/B testing with statistically sound methodologies, analyze individual ISP performance, and consider how factors like content balance and list hygiene influence your metrics. Always prioritize recipient experience and long-term sender reputation.

Why do all-image emails have higher open rates and are open rates a reliable KPI? - Content - Email deliverability - Knowledge base

When analyzing email campaign performance, it's common to see curious discrepancies. One such observation is that all-image emails sometimes report higher open rates compared to their text and image counterparts. This can be puzzling, especially when the goal is genuine engagement and conversions. It leads to a fundamental question about the reliability of open rates as a key performance indicator (KPI) for email marketing efforts.

Initially, one might assume that the visual appeal of an all-image email drives more recipients to open. However, the mechanism by which email opens are tracked introduces a significant nuance. Open rates are typically recorded when a tiny, invisible tracking pixel (a 1x1 pixel image) embedded in the email loads. If images are blocked by default in an email client, that pixel won't load, and the open won't be counted.

This leads to a paradox: while an all-image email might appear to have a higher open rate, it may not reflect actual human engagement or a better user experience. In fact, it could indicate a forcing mechanism, where users are compelled to load images just to view any content at all. Understanding this distinction is crucial for accurate performance measurement.

The illusion of higher open rates

The higher open rates for all-image emails are often an artifact of how email clients and users interact with messages, rather than a true measure of superior engagement. When an email is composed solely of images, recipients using clients that block images by default (which many do, for security and privacy reasons) see a blank or broken message. To view the content, they must explicitly enable image loading. When they do, the tracking pixel loads, and an email open is recorded.

This can inflate open rates. If a user *must* load images to see anything, they'll generate an open record, even if they quickly close the email once the images render. This isn't a sign of strong interest, but rather a necessary step to even preview the email's content. A hybrid email, with a balance of text and images, would allow users to get the gist of the message without needing to load images, meaning only those genuinely interested might enable them, potentially leading to a lower, but more accurate, reported open rate.

Additionally, some email service providers (ISPs) and anti-spam systems pre-fetch content, including images, to scan for malware or optimize delivery. This automatic pre-loading of images can trigger the tracking pixel and register an open without the recipient ever seeing the email. This is especially true for all-image emails, as there's no text content to parse without loading the images first. Such technical factors further distort the true open rate metric.

Why open rates are not a reliable KPI

The reliance on open rates as a primary KPI has been increasingly challenged, particularly with privacy-focused updates like Apple Mail Privacy Protection (MPP). MPP, for example, pre-loads all images for many users, regardless of whether they actually open the email. This action automatically triggers the tracking pixel, leading to artificially inflated open rates that don't reflect genuine recipient engagement. Consequently, a high open rate in this context becomes a misleading metric, as it fails to differentiate between an interested reader and an automated pre-load.

Before these privacy changes, open rates could offer some insight into subject line effectiveness or list health. However, in today's landscape, the reported open rate is simply not accurate. It cannot definitively tell you if a human eye actually saw your email. Therefore, using it as the sole or even primary indicator of campaign success can lead to flawed marketing strategies and misallocated resources. It's a metric, but its utility as a KPI, especially for gauging human engagement, is severely diminished.

Relying heavily on open rates might lead marketers to optimize for the wrong things, such as creating email formats (like all-image emails) that artificially inflate this metric but provide a poor user experience. This can inadvertently harm sender reputation and long-term deliverability if recipients mark such emails as spam due to their unreadable nature without image loading. The focus should always be on what drives actual value and engagement from the recipient, not just a numerical bump in a flawed metric.

The problem with open rates

Technical Inflation: Auto-pre-fetching by ISPs and anti-spam filters load images, registering opens without human interaction.
Privacy Features: Apple Mail Privacy Protection (MPP) automatically loads images, rendering traditional open tracking unreliable. This is discussed in detail in our article on how AI assistants and MPP impact email open rates.
User Experience: Users may enable images out of necessity to see content, not genuine interest.

Shift your focus to true engagement metrics

Instead of focusing solely on open rates, a more holistic approach to email analytics is necessary. Click-through rate (CTR) has emerged as a more reliable metric for gauging engagement, as it directly indicates that a recipient interacted with the email's content by clicking a link. This shows genuine interest and intent, which is far more valuable than a passive open. Another excellent metric is the click-to-open rate (CTOR), which measures clicks among those who opened the email. This helps you understand how engaging your content is after the initial open. Our guide on why email clicks decline despite high open rates dives deeper into this.

Beyond clicks, the true measure of email marketing success lies in conversion metrics: purchases, sign-ups, downloads, or any other desired action taken by the recipient. These metrics directly impact your business goals and provide tangible evidence of return on investment. If an email has a high open rate but zero conversions, its effectiveness is questionable. Therefore, optimizing for lower-funnel metrics like conversions and revenue is far more impactful than chasing inflated open rates.

Furthermore, factors like bounce rate and unsubscribe rate offer insights into list hygiene and content relevance. A high bounce rate indicates deliverability issues or an outdated list, while a high unsubscribe rate suggests that your content isn't resonating with your audience. These metrics, combined with engagement metrics, provide a more complete picture of your email program's health and effectiveness. For more on this, check out our insights on how opens should be used as a metric.

Open rate vs. actual performance

While an all-image email may show a statistically higher open rate, this doesn't necessarily translate to better performance where it truly matters: clicks, conversions, and revenue. The inflated open rate can be a deceptive metric, often a result of forced image loading or pre-fetching mechanisms rather than genuine recipient interest.

Metrics that matter more

Click-Through Rate (CTR): Measures active engagement with your content.
Click-to-Open Rate (CTOR): Indicates how engaging your content is for those who do open.
Conversion Rate: The ultimate measure of campaign ROI.
Revenue Per Email: Directly quantifies the financial impact.

Best practices for email content and tracking

For optimal email deliverability and recipient engagement, it's generally not advisable to send all-image emails. Such emails can trigger spam filters, especially if they contain little to no text content. Mailbox providers (ISPs) often view image-only emails with suspicion, as they are a common tactic used by spammers to hide malicious links or evade text-based content filters. This can lead to your emails being directed to the spam folder, regardless of your sender reputation, hurting overall email deliverability.

From an accessibility standpoint, all-image emails are a significant barrier. Screen readers cannot interpret images without proper alt-text, and even then, a heavily image-dependent email can be difficult to navigate. This excludes a segment of your audience and can lead to a negative user experience. Providing a balanced email design with a good text-to-image ratio ensures that your message is readable and accessible to everyone, regardless of their email client settings or assistive technologies.

To improve overall campaign performance, focus on creating engaging subject lines to entice opens (if still using it as a secondary metric) and compelling content that encourages clicks and conversions. Implement clear calls to action and ensure your emails are responsive across all devices. Regularly monitor your click-through rates, conversions, and revenue, as these metrics provide a more accurate reflection of your campaign's success. Additionally, maintaining good list hygiene and sender reputation is paramount. You can explore blocklist monitoring to ensure your emails are not being flagged by anti-spam systems.

For those still trying to accurately measure email open rates without relying on image pixels, it is a challenge. Many marketers are exploring alternative tracking methods or adjusting their interpretation of open data. The key is to adapt your measurement strategy to the evolving email ecosystem and prioritize metrics that provide actionable insights into your marketing objectives.

Image vs. text in email deliverability and accessibility

All-image emails

Inflated Opens: Higher reported open rates due to forced image loading or pre-fetching.
Deliverability Risk: Higher chance of hitting spam filters or being sent to the junk folder, as discussed in are image-only emails bad for deliverability.
Accessibility Issues: Difficult for screen readers and users with image blocking.

Text + image emails

Accurate Opens: Opens are more likely to represent genuine interest when text is immediately visible.
Improved Deliverability: Lower risk of spam flagging, as content is readable without images.
Enhanced Accessibility: Accessible to all users, regardless of image settings or screen readers.

Views from the trenches

Best practices

Prioritize engagement metrics like CTR and conversions over raw open rates to gauge true campaign success.

Design emails with a balanced text-to-image ratio to ensure readability and accessibility for all recipients.

Always include relevant alt-text for all images to provide context, even if images are blocked.

Monitor individual ISP performance to identify specific pre-fetching or image loading behaviors that may skew your open rates.

Common pitfalls

Relying solely on open rates as a primary KPI, especially in the age of Apple MPP and pre-fetching technology.

Sending all-image emails that force recipients to load images, leading to a poor user experience and potential spam flagging.

Ignoring other vital metrics such as click-to-open rates, conversions, and revenue, which provide deeper insights.

Failing to segment your audience or personalize content, which can impact engagement and deliverability.

Expert tips

Use A/B testing thoughtfully, ensuring statistical randomization of groups to avoid erroneous assumptions about outcomes.

Leverage a data scientist or BI analyst to analyze cohort variances and ensure test results are statistically significant.

Focus on the long-term health of your sending reputation rather than short-term vanity metrics like inflated open rates.

Consider a balanced content approach, showing essential information in text while using images to enhance the visual appeal.

Marketer view

Marketer from Email Geeks says they've observed that all-image emails consistently get 10-15% higher open rates than text and image versions, despite the latter having better click-to-open and revenue performance.

2019-09-10 - Email Geeks

Expert view

Expert from Email Geeks says that a significant number of people do not load images by default, and sending an all-image email forces them to load images to read the content, thus inflating reported 'opens' which are merely image loads.

2019-09-10 - Email Geeks

Optimizing beyond the open

While an all-image email may appear to boost open rates, this often results from technical factors and user behavior rather than genuine engagement. Open rates, especially after privacy updates like Apple MPP, are no longer a fully reliable KPI for email campaign success. They can be a useful diagnostic metric for subject line testing or trend analysis, but they shouldn't be the sole focus for measuring performance.

For a comprehensive understanding of your email marketing effectiveness, shift your focus to metrics that indicate active recipient engagement and direct business impact. Prioritize click-through rates, click-to-open rates, conversions, and ultimately, revenue. By adopting a more nuanced analytical approach and designing emails that are both engaging and accessible, you can ensure your email program truly delivers value.