Optimise your images

Large, unoptimised images are one of the most common causes of slow-loading emails and poor mobile experiences. This article explains the right formats, dimensions, and tools to use so your images load fast and look sharp everywhere.

Why image optimisation matters

• Speed: slow-loading images cause readers to abandon your email before it fully renders, especially on mobile connections.
• File size limits: Flexmail's media library has a 2MB limit per file. Unoptimised images from a camera or design tool routinely exceed this.
• Deliverability: emails with very large total file sizes can be clipped by email clients like Gmail, cutting off your content.

Choose the right file format

JPEG

Best for photographs and images with many colours and gradients. Save at 80-85% quality for a good balance of file size and visual quality. Use JPEG for: product photos, event photos, banner images, and any photographic content.

PNG

Best for images with sharp edges, text, logos, or transparency. PNG preserves detail that JPEG compression blurs. Use PNG-8 instead of PNG-24 where the colour depth allows. Use PNG for: logos, icons, screenshots, and graphics with text.

GIF

Use only for animated images. Keep animated GIFs short, small in dimensions, and with a limited colour palette to control file size. See 'Animated images in emails' for more guidance.

Resize before uploading

Email images don't need to be the same resolution as print images. A standard email is 600px wide, so an image wider than 1200px (for 2x/Retina screens) is more than you'll need. Resizing to the actual display dimensions before uploading dramatically reduces file size without any visible quality loss.

Compress your images

Even after choosing the right format and resizing, running your images through a compression tool can reduce file sizes by another 30-70% with no visible quality loss. Useful tools:

• Squoosh (squoosh.app): browser-based, shows a before/after comparison
• TinyPNG / TinyJPG (tinypng.com): simple drag-and-drop compression for PNG and JPEG

• ImageOptim (imageoptim.com): Mac app for batch compression

  
  

Next steps

• See 'The media library' to manage uploaded images in your account.
• See 'Add an image' to insert images into a message.
• See 'Animated images in emails' for guidance on using GIFs.

Related articles