What is the optimal image file size for emails to avoid spam filters and ensure fast loading times?

Summary

Optimizing image file size for emails is critical for deliverability, loading times, and user experience. Experts and marketers recommend balancing image quality with file size by using appropriate file formats (JPEG, PNG, WebP), compressing images, and resizing them to fit the display area. While some suggest an overall email size of under 100KB to avoid Gmail clipping, others aim for under 500KB or even allow up to 2MB. Using CDNs, lazy loading, and tools like TinyPNG/ImageOptim are also advised. Key considerations include responsive design, testing across email clients, and understanding the impact of file size on carbon footprint.

Key findings

  • File Format: Use JPEG for photos, PNG for graphics with transparency, and consider WebP for enhanced compression.
  • Compression: Compress images to reduce file size without significant quality loss using tools like TinyPNG or ImageOptim.
  • Total Email Size: Target a total email size (HTML, images, text) under 100KB-500KB to avoid clipping and ensure fast loading; 102KB to avoid Gmail clipping.
  • Deliverability Impact: Large images and overall email size can trigger spam filters and negatively impact sender reputation.
  • Loading Time: Optimized images and smaller overall size significantly improve email loading times.

Key considerations

  • Image Dimensions: Resize images to match the intended display area to minimize file size.
  • Responsive Design: Implement responsive design techniques and provide smaller image options for mobile devices.
  • Testing: Thoroughly test emails across different email clients and devices to ensure proper display and functionality.
  • CDN and Lazy Loading: Consider using a Content Delivery Network (CDN) to host images and implement lazy loading to improve loading times.
  • Optimize for Region: If sending worldwide, consider further optimizing or removing frames to accommodate varying internet speeds.

What email marketers say
11Marketer opinions

Optimizing image file size for emails is crucial for avoiding spam filters, ensuring fast loading times, and improving overall deliverability. Best practices include using appropriate file formats (JPEG for photos, PNG for graphics), compressing images to reduce file size, and resizing images to fit the intended display area. Keeping the total email size (including HTML and images) under 100KB-500KB is recommended to prevent clipping and improve the user experience. Load time and carbon footprint are also factors to consider. CDNs, lazy loading, and image optimization tools can also aid in creating optimized emails.

Key opinions

  • File Format Matters: Use JPEG for photos and PNG for graphics to optimize image quality and file size.
  • Compression is Key: Compress images to reduce file size without sacrificing too much quality. Tools like TinyPNG and ImageOptim can help.
  • Total Email Size: Aim to keep the total email size (HTML, images, text) under 100KB-500KB to avoid clipping and improve loading times. Although some suggest up to 2MB is ok.
  • Deliverability Impact: Optimizing images improves deliverability and sender reputation, preventing emails from landing in the spam folder.
  • Responsive Design: Create responsive versions of images that load faster on mobile devices.

Key considerations

  • Image Dimensions: Resize images to fit their intended display area to prevent unnecessary file size.
  • Testing: Test emails with different image sizes and email clients to ensure optimal display and deliverability.
  • CDN: Consider using a Content Delivery Network (CDN) to host images for faster loading times.
  • Lazy Loading: Consider lazy loading of images in your emails
  • Balance Quality and Size: Balance image quality with file size to ensure a good user experience without compromising deliverability.
Marketer view

Email marketer from Quora user Jane Doe explains that images should be optimized to be as small as possible without sacrificing visual quality. She notes that using tools for compression and adjusting dimensions can significantly reduce file size and improve email loading times.

May 2023 - Quora
Marketer view

Email marketer from HubSpot responds that optimizing images through compression and using appropriate dimensions is crucial for email deliverability. Reducing file size ensures faster loading and a better user experience, which can positively impact sender reputation and prevent emails from landing in the spam folder.

May 2022 - HubSpot
Marketer view

Email marketer from Reddit user u/EmailPro2020 responds that keeping the total email size, including images, below 500KB is a reasonable target. He adds that testing emails with different image sizes and email clients is essential to ensure optimal display and deliverability.

December 2024 - Reddit
Marketer view

Marketer from Email Geeks shares that file size often affects Gmail clipping based on code, not images. Overall weight was more of a factor when internet connections weren’t as fast. Image optimization is always a good practice. Responsive versions with smaller options can load faster on mobile, and testing is recommended.

October 2021 - Email Geeks
Marketer view

Email marketer from StackOverflow user User456 says that while there's no hard limit, best practice is to keep the total email size under 2MB, including all images and HTML, to prevent deliverability issues. They advise balancing image quality with file size and using image optimization tools.

February 2024 - StackOverflow
Marketer view

Email marketer from Mailjet explains that optimizing images for email involves using the correct file format (JPEG for photos, PNG for graphics), compressing images to reduce file size without sacrificing quality, and resizing images to fit the intended display area. This helps to minimize loading times and avoid potential spam triggers.

August 2023 - Mailjet
Marketer view

Email marketer from EmailToolTester responds that using tools such as TinyPNG or ImageOptim is key in compressing images without losing quality which helps to improve email loading times. They recommend resizing images before uploading them to your email marketing platform.

April 2024 - EmailToolTester
Marketer view

Email marketer from Campaign Monitor shares that keeping total email size under 100KB, including images, helps ensure fast loading and reduces the risk of emails being clipped by email clients like Gmail. They advise optimizing images and using appropriate compression techniques.

July 2021 - Campaign Monitor
Marketer view

Marketer from Email Geeks explains file size is a best practice for load time and it is generally fine to exceed 1MB within reason, especially if it is US only. If it is worldwide, consider removing some frames.

March 2024 - Email Geeks
Marketer view

Marketer from Email Geeks mentions load time and your carbon footprint are also impacted by file size.

July 2021 - Email Geeks
Marketer view

Email marketer from EmailGeekForum user EmailGuru explains that using a Content Delivery Network (CDN) to host images can help to reduce the load on your server and improve email loading times for recipients. They also advise to use lazy loading for images to improve the initial loading speed.

June 2023 - EmailGeekForum

What the experts say
1Expert opinion

Laura Atkins from Word to the Wise emphasizes that image optimization is critical for email deliverability. Large images can trigger spam filters, and slow loading times can hurt engagement. Vital elements include appropriate file formats, compression, and resizing.

Key opinions

  • Deliverability: Optimizing images is essential for email deliverability.
  • Spam Filters: Large images can trigger spam filters.
  • Engagement: Slow loading times negatively impact engagement.

Key considerations

  • File Formats: Use appropriate file formats for images.
  • Compression: Compress images to reduce file size.
  • Resizing: Resize images appropriately.
Expert view

Expert from Word to the Wise, Laura Atkins, explains that optimizing images is essential for email deliverability. Large images can trigger spam filters, and slow loading times can negatively impact engagement. Using appropriate file formats, compression, and resizing images are all vital elements.

July 2024 - Word to the Wise

What the documentation says
6Technical articles

Multiple sources indicate that optimizing image file sizes is crucial for email deliverability and loading times. Gmail clips emails exceeding 102KB total size. While there's no single optimal size, aiming for under 1MB is generally recommended, but smaller is better. Choosing the right format (JPEG, PNG, or WebP) and using compression techniques are vital. Responsive images and proper resizing also contribute to performance. Consider using CSS instead of images where possible.

Key findings

  • Gmail Clipping: Gmail clips emails larger than 102KB (total size).
  • Format Matters: Choosing the right image format (JPEG, PNG, WebP) is critical for file size and quality.
  • Compression: Image compression is essential to reduce file size.
  • Performance Impact: Reducing image size improves loading times and user experience.

Key considerations

  • Total Size Goal: Aim for under 1MB per email, but smaller is better (target around 100kb).
  • Responsive Images: Use responsive images to adapt to different screen sizes.
  • Resizing: Ensure images are appropriately sized for their display area.
  • CSS vs Images: Consider using CSS instead of images where possible to reduce file size.
Technical article

Documentation from Microsoft provides some best practices that include compressing images, choosing the correct format (JPEG or PNG), and using the Picture Manager to resize your images to the desired dimensions. This helps reduce the size of your emails.

December 2021 - Microsoft Support
Technical article

Documentation from Email on Acid shares that while there's no single 'optimal' image size, aiming for under 1MB is a good starting point, but far smaller is better. They discuss how using optimized JPEG or PNG files, depending on the image type, and ensuring images are appropriately sized for their display area can improve deliverability and loading times.

April 2024 - Email on Acid
Technical article

Documentation from W3C explains that reducing image size can significantly improve website and email loading times. It is important to select the correct image format, use appropriate compression techniques, and resize images to the optimal dimensions.

December 2021 - World Wide Web Consortium
Technical article

Documentation from Litmus explains Gmail clips emails larger than 102KB, so keeping your total email size below this limit—including HTML, text, and images—is crucial. They recommend optimizing images aggressively and using CSS instead of images where possible.

December 2022 - Litmus
Technical article

Documentation from Google Developers states that optimizing images for web and email involves choosing the right format (JPEG, PNG, or WebP), compressing images to reduce file size, and using responsive images to adapt to different screen sizes. This improves performance and user experience.

January 2025 - Google Developers
Technical article

Documentation from Mozilla explains that choosing the correct image format (JPEG for photographs, PNG for graphics with transparency) is vital to ensuring a low file size while retaining sufficient image quality. They elaborate on how different image formats handle compression and color depth.

June 2022 - Mozilla Developer Network