User Guide: Email File Size

When setting up emails, your main goal is usually content that resonates with your audience. Elements like subject lines, calls-to-action (CTAs), and the effectiveness of segmentation or personalization often take center stage during the design process.
However, there are two crucial factors that are frequently overlooked: email file size and load times.

While it might not be the most exciting aspect of email (and multi-channel) marketing, managing file size is vital for providing a seamless user experience. Large file sizes can strain bandwidth needed to download and view your email. If your recipients are unable to quickly load your email, especially on mobile devices, they're less likely to engage or convert.

Loading times depend on several factors, such as :

  • email service provider limits
  • the type of content in the email
  • the length of the email
  • the number, format and size of images used within the email (uncompressed images, animated GIFs, ...)
  • coding style being used (HTML, CSS, JS, ...)
  • use of custom fonts
  • the recipient's device
  • network capabilities

Below is a guide to help you determine the ideal and maximum email file size and improve load times.

 

Ideal Email File Size

  • General Best Practice: The ideal size for an email is typically 100 KB or less.

    • This size ensures fast loading times across different devices and networks.

    • Emails larger than this may cause slow loading, especially for users on mobile devices or slower connections.

  • Heavy Content Emails: If your email contains rich media like images or embedded elements, try to keep the size below 500 KB. Anything larger may cause loading issues or delays, especially for mobile users.

 

Maximum Email File Size

Provider Limits: Most email providers like Gmail, Yahoo, and Outlook impose a limit on the total size of the email, including attachments.

  • Gmail: 25 MB (combined size of attachments and body).

  • Outlook: 20-25 MB (depending on version).

  • Yahoo: 25 MB.

However, email body size (HTML content, text, and images) is often recommended to stay below 1 MB for efficient delivery and user experience.

 

Impact of Email Size on Loading Times

  • Smaller Emails (Less than 100 KB): These typically load almost instantly, even on slower internet connections, and work well across devices including mobile.

  • Medium Emails (100 KB - 500 KB): May take slightly longer to load, especially if images or embedded content are not optimized. Mobile users on data connections may notice a delay.

  • Larger Emails (500 KB - 1 MB+): Can cause significant loading delays, particularly for users on slower connections. Images may take time to appear, and recipients may lose interest before the content fully loads.

  • Very Large Emails (1 MB+): Likely to be flagged by some email clients or filtered into spam. These emails may also fail to load properly or appear truncated due to email client limitations.

 

Optimization Tips

  • Use Compressed Images: Compress images before adding them to emails. Tools like TinyPNG or ImageOptim can help reduce file size without sacrificing quality.

  • Minimize Embedded Media: Limit the use of embedded videos or GIFs, as they can significantly increase file size. Consider using clickable links to host videos on external platforms.

  • Clean HTML Code: Ensure your email’s HTML code is clean and free of unnecessary elements, which can bloat the file size.

  • Use Web Fonts Sparingly: Web fonts can increase file size, so limit the number of custom fonts or use system fonts when possible.

 

Testing

Preview and Test: Before sending, always test your emails across various devices and email clients to see how the size impacts loading times. Use tools like Email on Acid to check performance under different conditions.

 

Note: By keeping email file size within recommended limits and optimizing content, you can ensure fast loading times and a better user experience, which can ultimately lead to higher engagement rates.