What are the advantages and disadvantages of hosting email images on Amazon S3 versus CloudFront, and how does it impact deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jul 2025
Updated 19 Aug 2025
7 min read
When building emails, one crucial decision involves where to host images. Amazon S3 and Amazon CloudFront are popular choices, but understanding their nuances is key to optimizing email performance and ensuring strong deliverability. While both are part of Amazon Web Services (AWS) and work well for serving content, they serve different primary functions. S3 is object storage, designed for durability and scalability, while CloudFront is a content delivery network (CDN) that caches content at edge locations globally to reduce latency. This distinction has implications for how quickly images load for your recipients and, indirectly, for your email deliverability metrics.
Understanding Amazon S3 and CloudFront basics
Amazon S3 (Simple Storage Service) is fundamentally an object storage service. It's designed to store and retrieve any amount of data from anywhere on the web, making it a highly scalable and durable solution for hosting static assets like email images. When you host images directly on S3, they are served from a single AWS region, which means users geographically closer to that region will experience faster load times than those further away.
Amazon CloudFront, on the other hand, is a content delivery network. It works by caching your content (like images hosted on S3) at multiple global edge locations. When a user requests an image, CloudFront serves it from the nearest edge location, significantly reducing latency and improving loading speeds, especially for a geographically dispersed audience. This setup is generally recommended by AWS for delivering static content at scale, often used with S3 as the origin.
When considering the two, it's not always an either/or situation. Many organizations use S3 as the origin storage for their images and then use CloudFront to distribute those images globally. This combination leverages S3's reliable storage with CloudFront's speed and global reach. It’s also worth noting that both services offer robust security features, allowing you to control access to your image assets.
Performance and user experience considerations
The primary advantage of CloudFront over S3 for email images is speed. For recipients around the world, CloudFront significantly reduces the time it takes for images to appear in their inbox. This is due to its global network of edge locations, which cache content closer to the end user. Faster image loading provides a smoother user experience, particularly for image-heavy emails, which can indirectly influence engagement metrics.
While S3 is fast for users near the storage region, a global audience might experience noticeable delays if images are served directly from a distant S3 bucket. These delays, even if only tens of milliseconds, can impact how quickly a user perceives your email content. For web applications, a Content Delivery Network (CDN) is a cheap win to improve response time, and the same principle applies to email images, especially if your audience spans continents.
This performance difference primarily impacts the user experience, rather than directly affecting whether your email lands in the inbox. Email deliverability is more about sender reputation, authentication, and content quality. However, a poor user experience due to slow-loading images could subtly impact engagement, which in turn could influence your long-term sender reputation.
Amazon S3 direct hosting
Latency: Images are served directly from the S3 bucket's region, which can lead to higher latency for recipients far from that region.
Complexity: Simpler to set up, as it's just a storage bucket with public access settings.
Costs: Generally lower storage costs, but data transfer out (DTO) can become expensive with high traffic.
Amazon CloudFront CDN
Latency: Leverages a global network of edge locations to cache and serve content, significantly reducing latency.
Complexity: More complex initial setup due to distribution configurations, but offers more control over caching and security.
Costs: Higher initial costs compared to raw S3, but often more cost-effective for high-traffic, geographically distributed content due to lower DTO rates.
Impact on email deliverability and sender reputation
When it comes to direct email deliverability, the choice between S3 and CloudFront for image hosting typically has a minimal direct impact. Email deliverability is primarily influenced by your sending domain's reputation, email authentication (SPF, DKIM, DMARC), and the content of the email itself. However, there are indirect considerations.
One key aspect is the domain used to serve your images. Whether you use S3 or CloudFront, it is highly recommended to use a custom domain (often called a white-labeled domain) for your hosted images, rather than the default .s3.amazonaws.com or .cloudfront.net URLs. Using your own branded domain for image hosting helps build a consistent domain reputation across all aspects of your email. This can impact your email deliverability and reputation.
Email clients and spam filters generally don't block emails based solely on whether images are served from S3 or CloudFront, assuming they are properly configured and use HTTPS. However, if images fail to load due to hosting issues (e.g., incorrect permissions on an S3 bucket), it can negatively affect the user experience and potentially lead to recipients marking your emails as spam, which directly harms your sender reputation. For a broader understanding of how image hosting impacts deliverability, you might explore how S3 buckets and custom domains affect deliverability. If image loading times are extremely slow, it could also impact the firing of tracking pixels, which are often images themselves, leading to inaccurate open rate metrics.
Best practices for email image hosting
Use custom domains: Always serve images from a custom subdomain (e.g., images.yourdomain.com) for consistent branding and reputation control.
Optimize image sizes: Compress images to reduce file size, improving load times regardless of hosting method.
Ensure HTTPS: Always use HTTPS for image URLs. This enhances security and can positively influence deliverability. For more information, read about HTTPS/SSL for email images.
Monitor performance: Regularly check how quickly your images are loading for different geographic regions.
Cost and management implications
Cost is a significant factor in deciding between S3 and CloudFront. S3 generally has lower storage costs, and simple direct access from S3 might initially seem cheaper. However, as your audience grows and becomes more geographically diverse, the data transfer out (DTO) costs from S3 can quickly add up. CloudFront's DTO rates are typically lower than S3's for large volumes of traffic, making it more cost-effective for global content delivery at scale.
From a management perspective, hosting directly on S3 is simpler to set up and maintain. You essentially upload your images to a bucket and make them publicly accessible (or restrict access via more complex policies). CloudFront, while offering more features, involves setting up distributions, origins, caching behaviors, and potentially custom SSL certificates, which adds a layer of complexity. This complexity, however, offers greater control over content delivery, security, and caching strategies, as outlined by Amazon’s official documentation.
Security is another angle. While S3 provides robust storage security, CloudFront acts as a protective layer in front of your S3 bucket. It can offer additional security features like DDoS protection and Origin Access Identity (OAI) or Origin Access Control (OAC) to prevent direct access to your S3 bucket, ensuring content is only delivered via CloudFront. This added security can be crucial for protecting your assets and maintaining the integrity of your image links.
Views from the trenches
Best practices
Use CloudFront with a custom domain for global email campaigns to ensure rapid image loading and consistent branding.
Always optimize images for web before uploading, reducing file size without compromising quality.
Implement HTTPS for all image links to enhance security and build trust with email clients and recipients.
Regularly monitor your email engagement metrics, paying attention to how image loading speed might correlate with open and click rates.
Keep your S3 bucket permissions secure, only allowing public read access for served images via CloudFront.
Common pitfalls
Serving images directly from S3 for a global audience can lead to slow load times, impacting user experience and indirectly engagement.
Failing to use a custom domain for images, which can dilute your brand and make reputation management more complex.
Overlooking image optimization, leading to excessively large files that strain bandwidth and slow down email rendering.
Not implementing HTTPS for image links, which can trigger security warnings in some email clients and potentially harm deliverability.
Relying on default AWS URLs (like .s3.amazonaws.com), which ties your image reputation to a shared AWS infrastructure rather than your own domain.
Expert tips
Consider setting up CloudFront with multiple cache behaviors for different image types (e.g., small icons vs. large hero images) to fine-tune caching and expiry policies.
Use versioning in S3 for images if you frequently update them, allowing for rollbacks and preventing broken image links.
Explore AWS Lambda@Edge with CloudFront to perform image resizing or optimization on-the-fly, reducing the need for manual preparation.
If using an Email Service Provider (ESP), check if they offer built-in image hosting with CDN capabilities before setting up your own AWS infrastructure.
Always validate image URLs in your email templates before sending to avoid broken image placeholders in recipient inboxes.
Marketer view
Marketer from Email Geeks says that while CloudFront will definitely be faster than S3, the real question is how noticeable that speed difference will be for email images. If you have a global reach, using CloudFront can ensure faster loading of images and tracking pixels, which helps with reporting accuracy.
2019-07-31 - Email Geeks
Expert view
Expert from Email Geeks says that S3 is quite fast, and the latency advantages of CloudFront are typically in the order of a few tens of milliseconds, which might not make a significant user difference for email images compared to web applications where response time is critical.
2019-07-31 - Email Geeks
Making the right choice for your email images
For email images, choosing between Amazon S3 and CloudFront boils down to your specific needs for speed, global reach, cost efficiency, and management complexity. While S3 offers a straightforward and cost-effective solution for basic image hosting, CloudFront provides a significant boost in performance and additional security features, especially beneficial for campaigns targeting a worldwide audience.
Ultimately, the direct impact on email deliverability is minimal for both, provided you use custom domains and maintain proper image optimization and security practices. The indirect impact stems from user experience: faster loading times can lead to better engagement, which positively contributes to your sender reputation over time.
