What are the best practices for email image file sizes and design tradeoffs for user engagement?

Key findings

• Deliverability impact: For externally hosted images, larger file sizes primarily affect email load time, not direct deliverability. However, excessively large email sizes (including embedded images) can impact deliverability by triggering spam filters or causing truncation.
• Load time is critical: Slow loading emails, especially on mobile devices or poor network connections, lead to a poor user experience. This can result in users closing the email before images fully load, or even before engaging with the content, negatively affecting email click rates.
• Mobile audience: A significant portion of email opens occur on mobile devices, where data plans and network speeds can limit how quickly large images download. This makes optimizing image file sizes even more crucial.
• Engagement trade-off: The perceived benefit of more beautiful, higher-resolution images must be weighed against the potential loss of engagement due to slow loading. This applies particularly to email image sizes and promotions tab placement.

Key considerations

• Set size benchmarks: Aim for image files that are as small as possible without degrading quality, with a common recommendation of under 200 KB per image. This balance can be achieved through effective compression and choosing the right formats.
• Prioritize user experience: Even if deliverability is not directly affected, a poor loading experience directly impacts user engagement and conversion rates. User patience is limited, especially on mobile, so fast loading is paramount.
• A/B testing: The most definitive way to resolve internal debates about image quality versus size is to run A/B tests. Compare emails with highly optimized, smaller images against those with larger, more visually rich images and analyze engagement metrics.
• Image formats: Consider using modern image formats and appropriate compression. Some platforms recommend certain dimensions to ensure optimal rendering across various email clients and devices. Optimizing email images is crucial for effective email campaigns.

Key opinions

• Mobile experience matters: A significant portion of their audience views emails on mobile devices. Large images can cause frustration for these users, leading to them abandoning the email.
• Load time sensitivity: There's a strong belief that users, especially those not highly engaged, will not wait for large graphics to download.
• Data-driven decisions: Marketers prefer to use empirical data, such as A/B test results, to inform decisions regarding image optimization and resolve internal conflicts with design teams.
• Image optimization impact: While designers might dislike the aesthetic compromise, marketers understand the necessity of image optimization for broader user experience, as detailed in best practices for email images.

Key considerations

• Run A/B tests: Test variations with optimized versus non-optimized images to gather concrete data on how load times affect opens, clicks, and conversions.
• Educate design teams: Share data and case studies demonstrating the direct impact of load time on user behavior, emphasizing that aesthetic quality without performance optimization can be detrimental.
• Consider audience behavior: For less engaged audiences, the initial experience is paramount. A fast-loading email, even if slightly less visually perfect, might yield better overall engagement.
• Alternative solutions: Explore progressive loading techniques or dynamic content options that prioritize speed without completely sacrificing design aspirations. Understanding image-based email implications is important.

Key opinions

• Deliverability vs. load time: If images are hosted externally, their size primarily impacts load time for end users and generally does not affect deliverability. This distinction is crucial for managing expectations and priorities.
• User experience is key: The tradeoff for designers to make involves balancing aesthetic appeal with the potential for slower email loading. A visually appealing email might be a good tradeoff if it entices unengaged users, but this needs to be assessed from a user experience perspective, particularly regarding optimal image file sizes.
• A/B testing is essential: There is no reason not to A/B test different image optimization strategies. Even with small segments, a relatively high degree of confidence can be achieved if sampling is sufficiently random.
• Compromise solutions: Considering formats like larger interlaced PNG files can offer a compromise. While these might have bigger file sizes, they upload a degraded image first, improving the perceived loading speed.

Key considerations

• External image hosting: Always host images externally to minimize the email's overall size and avoid direct deliverability issues associated with large embedded files. This also relates to email file size and image hosting for Gmail.
• Quantify UX impact: Use data from A/B tests to demonstrate the tangible impact of load time on user engagement, such as time spent viewing or click-through rates, as noted by SalesEra on image quality affecting user engagement.
• Optimize image formats: Experiment with different image formats and compression techniques to find the optimal balance between visual quality and file size for various email clients and devices.
• Audience segmentation for testing: For super senders, testing with small, randomly sampled segments can still provide high confidence in results across the entire database.

Key findings

• Optimal dimensions: Most documentation recommends image widths between 600 and 1000 pixels for general email use, with signature images often smaller (e.g., 150 pixels tall, 300 pixels wide). Height typically has no strict limit.
• File size targets: A common recommendation is to keep individual image file sizes under 200 KB, with some suggesting even smaller for specific uses, to prevent slow loading.
• Resolution standards: A resolution of 72 DPI is generally considered best practice for web and email images, balancing clarity with file size efficiency.
• Compression importance: Documentation frequently advises using compression tools to reduce file size without significant loss of perceived quality. This helps mitigate negative impacts of large images.

Key considerations

• Content design: While visually appealing, image-heavy emails should be balanced with sufficient text content to aid deliverability and accessibility, as discussed regarding image-only emails.
• Accessibility: Always include descriptive ALT text for images. This ensures that even if images don't load or if recipients use screen readers, the content's message is still conveyed.
• Mobile responsiveness: Design images to be responsive, adapting their size and layout to different screen dimensions to ensure a consistent and positive user experience across devices.
• Email client compatibility: Test emails across various email clients (e.g., Gmail, Outlook, Apple Mail) to ensure images render correctly, as clients handle images and code differently. This is part of ensuring good email code quality and size impact.