How does the image to text ratio in email affect deliverability?

Key findings

• Accessibility concerns: Emails that are predominantly images can exclude users with visual impairments or those who have images blocked, making the content inaccessible. This directly impacts user experience and engagement.
• Spam filter influence: Some legacy spam filters, like SpamAssassin, may assign higher spam scores to emails with a very high image-to-text ratio. However, the weight of this factor has decreased over time with modern filters focusing more on sender reputation and engagement signals.
• Reputation impact: If recipients cannot easily read or understand an image-heavy email, it can lead to negative actions such as deletions without opening or marking as spam, which directly harms your sender reputation and deliverability.
• Loading times: Large or numerous images increase email file size, leading to slower loading times. This can deter recipients, especially on mobile devices or slow internet connections, potentially impacting engagement.
• Content readability: Too many images can make an email difficult to skim and quickly understand its purpose without images enabled, reducing the effectiveness of your message.

Key considerations

• Balance content: While there's no universally strict rule, many recommend a balance of 60% text to 40% images. This ratio helps ensure readability and reduces potential spam flagging.
• Always use alt text: Crucially, always include descriptive alt text for all images. This ensures your message is conveyed even if images don't load and is vital for accessibility tools.
• Optimize image sizes: Compress images to reduce file size without sacrificing quality. This improves loading times and overall email performance, which can indirectly affect engagement and deliverability. Read more about how email image sizes affect deliverability.
• Plain text version: Ensure you provide a robust plain-text version of your email. Many email clients and spam filters refer to this, and it's essential for accessibility.
• Test thoroughly: Always test your emails across various clients and devices, with and without images enabled, to understand the user experience and potential deliverability impact.

Key opinions

• User experience first: Many marketers prioritize the recipient's experience, arguing that poor readability due to too many images leads to disengagement, regardless of whether it lands in the inbox.
• Accessibility matters: The exclusion of visually impaired users or those with images turned off is a significant concern for ethical and effective marketing. This can be mitigated by ensuring proper email template design.
• Indirect deliverability impact: While not always a direct spam trigger, a frustrating user experience (like unreadable image-only emails) can lead to higher spam complaints or low engagement, which negatively impacts sender reputation and inbox placement.
• Modern filter focus: Some marketers note that ISPs like Google and Microsoft rely less on content-based filtering (like image-to-text ratio) and more on behavioral signals and sender reputation.
• Alt text as a fallback: The importance of robust alt text is consistently highlighted as a way to mitigate the risks associated with image-heavy emails, providing a text-based alternative.

Key considerations

• Don't send image-only emails: This is a near-universal recommendation due to deliverability risks, accessibility issues, and poor user experience. It's often associated with spammer tactics.
• Prioritize clarity: Ensure the core message is conveyed through text, even if images are disabled. Calls to action (CTAs) should ideally be text-based buttons.
• Consider email content strategy: Evaluate if the content *needs* to be so image-heavy. Often, a more balanced approach with effective copywriting can be more impactful.
• Monitor engagement: Pay close attention to metrics like open rates, click-through rates, and spam complaints. These are stronger indicators of content performance than just the image ratio itself.
• Test with an email deliverability tool: Use an email deliverability tester to get insights into how your email, including its content and image ratio, performs across various inboxes.

Key opinions

• Reputation is paramount: Experts largely agree that sender reputation, built on consistent sending practices and positive engagement, outweighs content-specific ratios for deliverability. This includes proper DMARC, SPF, and DKIM authentication.
• Content is secondary to behavior: While content can trigger filters, behavioral signals (like opens, clicks, replies, and spam complaints) are more influential for ISPs than rigid content rules. A poor image-to-text ratio that leads to low engagement is where the problem lies.
• Image-only emails are risky: Despite a decreased direct impact, sending emails composed almost entirely of images is still widely considered a bad practice due to its historical association with spammers and poor user experience.
• Alt text is non-negotiable: The importance of comprehensive alt text is a consistent message among experts, not just for accessibility, but as a fallback for content when images are blocked by default. This is one of the technical solutions for improving deliverability.
• SpamAssassin's limited relevance: Some experts point out that while SpamAssassin has a rule for image-to-text ratio, its use is not as widespread as it once was, and the specific score attributed to this rule is often low.

Key considerations

• Focus on engagement: Design emails that encourage positive recipient actions (opens, clicks). If an image-heavy design hinders this, it will eventually impact deliverability more than the ratio itself.
• Ensure fallback content: Always ensure there's sufficient plain text in your email, especially for critical information and calls to action, even if images are present. This includes providing a robust plain text version.
• Monitor spam trap hits: If a high image-to-text ratio leads to poorer list hygiene and spam trap hits, this will severely damage deliverability, regardless of content.
• Don't trigger classic spam signals: While ratios may be less critical, combining high image ratios with other spammy characteristics (e.g., suspicious links, common spam phrases, or poor email code quality) significantly increases risk.

Key findings

• Accessibility standards: Many email and web standards emphasize the need for accessible content, which includes using descriptive alt text for images to ensure content is available to screen readers and when images are blocked.
• User engagement metrics: ISP documentation (e.g., Google Postmaster Tools) heavily emphasizes the role of user engagement (opens, clicks, spam complaints) in determining sender reputation and inbox placement, indirectly favoring content that is easy to consume.
• Content analysis tools: Some older or open-source spam filtering software, like SpamAssassin, explicitly include rules that penalize emails with an imbalanced image-to-text ratio, although their weight may vary.
• File size limitations: Documentation often advises optimizing email file size. Since images contribute significantly to file size, this implicitly encourages a more text-lean, optimized image strategy to avoid slow loading or truncation.
• Sender best practices: General best practices from ISPs suggest sending high-quality, relevant content that minimizes triggers for spam filters, which can include unusual content ratios.

Key considerations

• Adhere to HTML standards: Ensure your HTML structure is clean and valid. This includes proper use of image tags with alt attributes, which helps parsing by both email clients and filters.
• Review ISP guidelines: While not always explicit on ratios, documentation from major ISPs (e.g., Gmail, Outlook) often provides general best practices for content and design that indirectly support a balanced approach. This can help with troubleshooting issues related to SpamAssassin scores.
• Include a text-only alternative: MIME multipart emails should always include a plain text version that accurately reflects the HTML content. This is a fundamental email standard that enhances compatibility and deliverability.
• Avoid suspicious image practices: Documentation often warns against tactics like hiding text in images to evade text filters, as this can severely impact sender reputation and lead to blocklisting.